They call him the "flashback merchant," but they do not know what they're saying. Tanjiro has more intelligence feats without flashbacks than he does with flashbacks.

1. During the Tsuzumi Mansion Arc, Tanjiro deduced the shifting layout of a constantly rotating, magical house. By tracking the scent of blood and demon musk through changing walls, he created a mental map of the labyrinth to navigate it.
2. In the very beginning of demon slayer, an untrained Tanjiro, who knew that Giyu outclasses him by far, formulated a multi-step trap by throwing a rock as a distraction, his hands, sprinted forward blindly to fool Giyu into thinking he was attacking, all while secretly having tossed his iron axe into the air, which nearly killed Giyu.
3. In Mount Natagumo, the Spider Mother demon was controlling dozens of In Mount Natagumo, the Spider Mother demon was controlling dozens of Demon Slayers like meat-puppet corpses, manipulating them via invisible threads. Cutting the threads was useless, as the demon's spiders would instantly reattach them. Tanjiro realized that trying to physically overpower or cut his way through his mind-controlled allies would only injure them so instead he grabbed the puppet-slayers and tossed them over the high branches of the surrounding tree to tangle the threads in the branches which in turn, caused them to slacken and making the puppets completely immobile.
4. Agaisnt Hantengu, Tanjiro was blown far away from Nezuko and Genya by Urogi and realizing his friends were in danger back at the house, Tanjiro analyzed Urogi’s anatomy mid-air and deduced that because Urogi is a flying creature, his body mass must be incredibly light to stay airborne. Tanjiro then tackled Urogi, locked his legs around the demon's torso and manipulated Urogi's wings to ride his sonic attack wave to fly straight back to the main field.
5. Agaisnt Gyutaro, Tanjiro was out of stamina, poisoned and cornered by him. And Gyutaro considered Tanjiro a completely broken, non-threat. So Tanjiro weaponized that arrogance and ffeigned complete helplessness, headbutted Gyutaro and secretly stabbed him with a kunai hidden in his hand, he literally created himself a one-in-a-million opening to nearly decapitate him
6. In the EDA, Tanjiro's body was breaking down from using Hinokami Kagura, which his muscles could not handle for prolonged periods. Needing to parry Daki's attack, he couldn't rely on Hinokami Kagura's offensive power of Water Breathing's low defensive speed, and so he subconsciously synthesized the two styles and used the defensive forms of water breathing to absorb the impact of the attacks, but imbued the strikes with the cutting power of Hinokami Kagura to save his stamina.
7. When fighting the Arrow Demon (Yahaba), Tanjiro was caught in invisible kinetic vector arrows that threatened to snap his limbs. He used the rotational kinetic force of his Water Breathing forms to wrap around the vectors to neutralize the physics of the pull and using the demon's own kinetic energy to amplify his final strike.
8. During his early training, Tanjiro struggled to find a way to break through an opponent's perfect defense. And so, Tanjiro abstractly connected his physical senseo f smell to conceptual logic by realizing that when an opponent leaves a fraction of a second's opening, their scent profile shifts slightly. He trained his brain to translate this scent into a visualized "opening thread" connecting his blade to the enemy's weak spot. He's effectively turning a raw sensory input into an extremely precise geometric striking path.

Do I need to say more? Tanjiro is one of the smartest if not THE smartest character of his verse. And I don't wanna hear anyone yapping about experience because that is not what battle IQ or intelligence stands for.

Doma first observes, "He's swinging his sword, but he's out of range. Too far away." Then he confidently thinks "See? You can't reach me at all?" At this point, Doma believed he was completely safe because he thinks Inosuke's attack cannot physically reach him.

Then the very next moment, blood appears across his face and he realizes, "He got me with a slash!" This line tells us that he didn't even realize he had already been hit. His realization comes only after the attack has already connected, meaning there was a delay between the slash landing and him consciously processing what happened. If Doma had perceived the attack in time, he would have reacted to the blade extending or attempted to evade.

You can also visibly see that the slash carved across Doma's eyes

Then in the last slide Inosuke says that this technique is new and that he doesn't have enough mastery over it yet which is why he missed his neck.

Just imagine a full potential Inosuke with maxed out physical stats and full mastery over this technique. He'd genuinely be putting in work against other demons with that technique if he can already do this to Doma.

EDIT: I forgot to add the panel of the first paragraph but that's what it says in the official english translation.

Tanjiro : Infinity Castle Arc, before he got STW & SS, so the only amp he has is his permanent mark.

Rengoku : Base form. This doesn't include his amp at the end of the fight against Akaza.

• OVERALL STRENGTH (PHYSICAL, LIFTING, STRIKING): Rengoku (3-0)

- While sprinting down the aisles of the Mugen Train to protect passengers from Enmu, the sheer force of Rengoku's movement and non-Breathing slashes caused multiple heavy passenger cars to visibly shake and lift off the tracks.

- In the movie, Rengoku swung his katana with enough force to launch Akaza backwards and sent him flying a large distance that made him crash into the deep forest line.

• TRAVEL SPEED & ATTACK SPEED: Rengoku (5-0)

- Rengoku has more consistent showings of how fast he can move in a straight line sprint. Such as the same feat of protecting the passengers from Enmu. Akaza in chapter 63, when Rengoku closed the distance on him, he praised how fast it was. Akaza has never been dishonest about what he praises so it is a reliable statement. Rengoku's also stated to be the 5th fastest running Hashira.

- For his attack speed, in both the movie and manga (Chapter 63, pages 3–5), Akaza spots Tanjiro, whom he despises for being weak, and immediately charges at him with killing intent, veins popping from his body. This punch is boosted by the momentum that he built from his high-speed dash, making it faster than a normal punch. Despite this, Rengoku instantly intercepted it with his Second Form: Fire Wheel when Akaza's fist was point-blank range from hitting Tanjiro, cleanly severing Akaza's arm, so this shows us that the technique outsped a velocity-amped punch from a blood lusted base Akaza.

• COMBAT & REACTION SPEED: Tanjiro (5-2)

- In Chapter 67, Akaza vows to "spill Tanjiro's brains," showing clear killing intent toward him. This carries into their rematch (Chapters 147–149), where Akaza consistently attacks with a serious expression and visible veins specifically at Tanjiro. After Tanjiro reminds him of his past in Chapter 149, Akaza becomes even more enraged, calling him "unpleasant" and relentlessly pressures him, but Tanjiro blocks or evades every attack and briefly clashes with him in the bottom of the panel from chapter 149, page 12.

• DURABILITY & ENDURANCE: Tanjiro (5-4)

- In chapter 152, Tanjiro took one of Akaza's afterglow shockwaves (his strongest technique) and was still able to move to fight Akaza. For clarity, this is is the same attack that had an already-exhausted Marked Giyu injured to the point where he couldn't move for a brief moment.

- In the EDA, before beheading Gyutaro, Tanjiro was impaired by Gyutaro's jagged poison-coated sickle that completely pierced through his lower jaw, two broken fingers on his left hand, and poison pumping directly through his bloodstream, which was actively shutting down his heart. Despite these, Tanjiro didn't stop and forced himself to grip his katana, unlocked his DS Mark and sliced off Gyutaro's head while his lower jaw was still impaled.

• STAMINA: Tanjiro (5-5)

- Fought Akaza longer than Rengoku. Then later on after recovering a bit more, still had the energy to go after Muzan.

• INTELLIGENCE: Tanjiro (5-6)

- In the ICA, Tanjiro completely deduced the mechanics of Akaza’s complex BDA. He realized the technique tracked "battle spirit" (malice, focus, and intent). By actively analyzing his own physiology he found a way to counter it.

- During the Tsuzumi Mansion Arc, Tanjiro deduced the shifting layout of a constantly rotating, magical house. By tracking the scent of blood and demon musk through changing walls, he created a mental map of the labyrinth to navigate it.

• BATTLE INTELLIGENCE: Tanjiro (5-7)

- In the very beginning of demon slayer, an untrained Tanjiro, who knew that Giyu outclasses him by far, formulated a multi-step trap by throwing a rock as a distraction, his hands, sprinted forward blindly to fool Giyu into thinking he was attacking, all while secretly having tossed his iron axe into the air, which nearly killed Giyu.

- When fighting the Arrow Demon (Yahaba), Tanjiro was caught in invisible kinetic vector arrows that threatened to snap his limbs. He used the rotational kinetic force of his Water Breathing forms to wrap around the vectors to neutralize the physics of the pull and using the demon's own kinetic energy to amplify his final strike.

- Tanjiro realized his legs were too exhausted to catch Hantengu, so he recalled Zenitsu's verbal description of Thunder Breathing mechanics, and he used that to calculate the exact muscle and oxygen distribution needed to use thunderclap and flash and invented his own attack by fusing it with Hinokami Kagura.

• ABILITIES & HAX QUALITY: Tanjiro (5-9)

- Enhanced sense of smell,
- DS mark,
- Precognition,
- Water Breathing,
- Hinokami Kagura,
- 22 total breathing forms,
- Water Breathing and Hinokami Kagura fusion.
- Hinokami Kagura and Thunder Breathing fusion.

• ATTACK POTENCY & DESTRUCTIVE CAPACITY: Rengoku (7-9)

Rengoku's 9th form carved up Akaza's body and is a visually massive explosive AoE attack.

• OFFENSIVE COMBAT: Rengoku (8-9)

- Rengoku had a more consistent offensive combat portrayal against a surpressed Akaza, as is it stated by the light novel that their techniques we're evenly matched. And Rengoku's offensive output was so massive with his 9th form that his single strike slashed through Akaza's blocking arms, carved entirely open his torso, and cut deep into his neck.

• DEFENSIVE COMBAT: Tanjiro (8-10)

- Tanjiro was consistently able to block and evade attacks from a bloodlusted Akaza, it was not until Akaza used afterglow, which is his strongest technique that he finally managed to land a hit on him.

• WINNER: EITHER WAY
• TANJIRO (MID DIFFICULTY)
• RENGOKU (EXTREME DIFFICULTY)

It genuinely NEEDS to be understood how Akaza was not trying agaisnt Rengoku.

In chapter 67, page 6, Akaza says the following to Muzan:

"As you commanded I killed one of the Hashira. All is well."

Muzan replies with:

"Akaza, you appear to be under a misconception. Why even bother to tell me you killed a mere hashira? it is only natural for a demon to defeat a human. What I seek is the annihilation of the entire demon slayer corps itself. We must kill every last one so they never sully my sight again."

This directly tells us that Akaza's mission was to kill every demon slayer there.

But Akaza was so obsessed with the idea of turning Rengoku into a demon that he was ready to go against what the Demon King assigned him to do just to achieve his own desire.

Akaza literally gives Rengoku breaks and stops attacking mid-exchanges just to keep on talking about how Rengoku should become a demon, that was literally the only thing he was yapping about the entire fight whenever he said something: praising his skills and trying to lure him into accepting his offer because it would be a shame to die with such potential. He even states in chapter 64, page 7 how he wants to fight with him forever.

So yeah he's trying to gaslight Rengoku into becoming a demon more than he is fighting seriously, and I don't think I need to repeat myself on Tanjiro's performance against a bloodlusted Akaza do I? Just know that if Rengoku is massively weaker than a bloodlusted Akaza who can't even hit Tanjiro, then Rengoku isn't doing any better.

Though Rengoku's 9th form may impose a threat to Tanjiro, that is the only thing that gives him a shot at standing a chance.

• Full Power (FP) Gyomei = Gyomei with all his amps (DS Mark, STW, Red Blade)
• Serious Doma = Serious Doma

(This is a comparison of what we've seen from them in the show (scaling), not a matchup between the two.)

I’ve said this many times before: in Chapter 170, Marked Gyomei indirectly references Yoriichi while speaking to Kokushibo. This clearly triggers Kokushibo, since we know how deeply traumatized he has been by Yoriichi. On the very next page, Kokushibo cuts him off mid-sentence and immediately goes for his neck, visibly enraged (vein popping from his neck, aggressive expression). Gyomei blocks the attack and proceeds to evenly exchange blows with him for the next four pages, with neither of them landing a hit.

From this, we can scale:

Angered Base Kokushibo ~ Marked Gyomei

This already places Marked Gyomei above Doma, since there’s no solid basis to assume an angered Base Kokushibo would be weaker than a serious Doma. However, the exact gap between Gyomei and Doma depends on how much stronger you believe an angered Base Kokushibo is compared to Doma but he definitely isn't weaker because not only Kokushibo still classifies as UM1 in his base form, and this is an enraged Kokushibo triggered by the thought of Yoriichi we're talking about, the same guy who Kokushibo's resentment towards lasted over than 400 years.

However we know that Kokushibo still isn't using his full power in terms of technique (long sword) or monster form (transformation) because he later on blitzes Gyomei in that form. But in terms of base form capability, setting aside vibe scaling and actually following what the narrative is showing us, he is physically fighting seriously if not going all out.

In Chapter 172, Marked Gyomei is also able to react to and evade Long Sword Kokushibo’s attacks. This Kokushibo is definitely more serious and engaged here because after struggling agaisnt Sanemi & Gyomei's coordination in chapter 171, Kokushibo states "Once I dispatch you two, the rest shall proceed easily.” The word "dispatch" means to end something as quickly and efficiently as possible.

Btw this is all pre-STW Gyomei. We don't see him much in action compared to before but we can scale it based on what we know of STW.

From Tanjiro’s explanation in Chapter 152, STW significantly enhances perception which allow the user to predict movements and evade attacks more effectively. Though it does not directly increase physical speed, the improved perception creates the appearance of increased speed in combat.

This is supported by when Akaza, who has no knowledge of STW thinks that Tanjiro "surpassed his speed," even though the actual change was perceptual rather than physical.

Before unlocking STW, Tanjiro was clearly inferior to Akaza but the boost of the STW was so significant that it changed Akaza’s perception of Tanjiro's speed which he he deemed to have surpassed his.

Since this effect is the same regardless of the user, it’s entirely reasonable to conclude that Marked + STW Gyomei would gain a similar advantage that would allow him to appear fast enough to surpass that specific angered Base Kokushbo from chapter 171 in "speed", considering they were already very close prior to that.

So if we're talking about in pure scaling:

FP Gyomei > Angered Base Kokushibo ~ Marked Gyomei > Serious Doma

(With the gap between Marked Gyomei & Doma depending on how much stronger you believe an angered Base Kokushibo is compared to Doma)

Though in a matchup, Doma's BDA could potentially act as an environmental counter to Gyomei’s ability to activate his mark, but that is just a matchup advantage that does not mean that he scales higher than Gyomei, and like I said, this is just a scaling comparison.

With that being said, Gyomei is the undisputed top 4 of the verse behind Kokushibo, Muzan, and Yoriichi.

Rengoku prevented Akaza from escaping with his strength despite Akaza actively trying to pull away. However, it doesn't prove that Rengoku was physically stronger than Akaa because the were circumstances that gave Rengoku an advantage:

Akaza's arm was buried deep inside Rengoku's torso, meaning he wasn't simply trying to overpower Rengoku's grip in a neutral contest but he first had to overcome the friction and resistance created by his own arm being lodged inside Rengoku's body while Rengoku squeezed his arm with both hands. Since multiple factors contributed to Akaza being unable to escape the feat shouln't be isolated as a pure "Rengoku overpowered Akaza" moment.

With that being said, the feat still scales Rengoku's strength extremely high because even with the positional advantage, Rengoku still had to generate enough force to prevent Akaza from freeing himself. If Akaza's raw physical strength had been overwhelmingly greater, then the positional disadvantage would not have mattered for long and he simply would've overpowered Rengoku's grip and pulled his arm out. So by logic, Rengoku's physical strength was close enough to contest Akaza's even though it doesn't mean it was superior.

So in terms of physical strength:

FP Akaza >~ Death Amp Rengoku > Marked Giyu

Yes, Akaza is utilizing his full strength, he has no reason not to when he's shown desperately trying to get away from the sunlight.

Given the fact that a death amp increases a character's stats overall, which is supported multiple times throughout the series by the following:

• A death-amped Shinobu became fast enough that Doma admitted he "couldn't predict her attacks," while also displaying enough physical strength to push him into the ceiling.
• Muichiro continued fighting after being cut in half
• Obanai states in chapter 189, page 17 that people become stronger when they're on the verge of death. Muzan likewise comments in chapter 193, page 1 on such.

With that in mind, there is no reason to isolate Rengoku's physical strength as the only attribute that increased. His other stats such as overall speed, durability, stamina, endurance, etc should have been amplified alongside his strength. Since his physical strength scales relative to a full-power, desperate Akaza through the restraint feat, his other amped physical attributes should logically scale to a similar level as well, roughly above the serious Akaza that Marked Giyu fought.

So in terms of overall scaling:

FP Akaza >~ Death Amp Rengoku > Marked Giyu

This is for those who think that experience is what makes Toji win.

"A demonic fighter equal to Toji Zenin"

The key word here is "fighter." A fighter refers to someone as a combatant, meaning the overall qualities that determine how effective they are in combat. Such things include physical ability, skill, instincts, battle IQ, experience, and any other factor that contributes to fighting ability.

Because of this, Toji's "advantage in experience" over Maki becomes irrelevant, or else that would be implying an advantage in combat ability, which in turn defeats the purpose of them being equal as fighters.

That is why the comparison itself already considers those things, because it compares the end result of all the combat relevant qualities combined (a fighter).

So the natural implication is that neither possesses a decisive combat advantage over the other due to experience, skill, battle IQ, or any other quality that defines someone as a fighter. If one did, then they simply wouldn't be equal fighters in the first place.

Since no clear edge can be established from the statement itself, you can’t reasonably assume one would win against the other in a stable way, and as a result, the most accurate baseline assumption is parity, meaning the matchup is evaluated as even unless there is a context that introduces a specific situational advantage for one of them.

Kokushibo's level

Not only Kokushibo is 2 ranks above Akaza in ranks, he says that he's the only Upper Moon capable of "fighting effectively". Whether you overlook that statement or not, the gap is still significant between him and Akaza.

Gyomei's level

Gyomei then goes on to indirectly reference Yoriichi, which is something that clearly got under Kokushibo's skin. You can literally see the vein popping out on his neck, as he doesn't let Gyomei finish his sentence and appears directly in front of him, then goes for his neck. At this point, Kokushibo genuinely wanted Gyomei gone.

Despite that, Kokushibo does not land a hit once, Gyomei parries his attack and the two clash evenly for the 2 next pages until Sanemi joins the fight.

Akaza, also the same dude who holds a grudge against Tanjiro and says he'll "spill his brains out," in chapter 67, page 11. Yet from Chapters 147-149, in their rematch, he can't land a single hit on him. It isn't until he uses Afterglow, which is his strongest technique that he finally hits him.

So a full power Gyomei slams Akaza with little to no difficulty while we're at it.

Sanemi & Giyu's feats

Sanemi is relative to that same Gyomei (there is no massive gap between them as fighters) that is because of how well they were able to coordinate against Kokushibo which led to Kokushibo struggling to keep up and get forced into pulling his Long Sword. Kokushibo even comments on how quickly they synchronize their attacks.

That level of coordination isn't possible if one fighter is significantly slower than the other because one would constantly fall behind, and the teamwork would completely fall apart. Like how Tanjiro could not properly assist base Giyu in combat against Akaza and his attempts literally amounted to nothing and Tanjiro just became a liability and has to watch them fight, which shows us that Tanjiro was not relative to that Giyu at that point of the story.

My point here is to show how being able to keep up with another's speed to coordinate in a 2v1 is a form of relativity.

Sanemi & Giyu's sparring match

The main basis people use to justify their equality.

First, Giyu can't fully evade Sanemi's first form and the best he can do is block it, with his sword getting chipped. On the other hand, Sanemi completely avoids Giyu's Fourth Form while being in the air and calls him "too slow."

Some people argue Sanemi only said that because he dislikes Giyu, but Sanemi hates demons far more than he dislikes Giyu (check his backstory,) yet when he fights Kokushibo, he openly acknowledges how fast Kokushibo is. If Sanemi is willing to admit the speed of someone he hates even more, why assume he was lying or taunting about Giyu being too slow? Maybe he said that because it actually is the case.

Sanemi & Gyomei

But even if you ignore all of that and still think Sanemi and Giyu were equal during the spar, Sanemi later says to Gyomei, "Good thing we trained together!" during their fight agaisnt Kokushibo. While the following is only an interpretation, it perfectly makes sense to assume that Sanemi, who was previously on Giyu's level via their sparring match, went to train with Gyomei, who is like I said before, a lot stronger than that.

The results of Sanemi training with Gyomei are shown through how they can effectively coordinate against Kokushibo, hence why Sanemi says "good thing we trained together!" during that same moment, because their "training together" is what allowed them to reach a level that is comparable to each other in terms of combat ability, shown through their effective coordination agaisnt Kokushibo.

Given the statements of the manga/anime, it is very easy to conclude that Akaza's Compass Needle functions much like an actual compass. That is because Tanjiro notes that Akaza's attacks land with incredible precision on his opponent, similar to how a compass needle aligns itself toward its point of attraction.

Compass Needle is also known to detect Akaza's opponent based on their fighting spirit so that his strikes adjust with accuracy regardless of their movements, also similar to how a compass constantly recalibrates itself to maintain its direction toward a magnetic field.

So basically, Akaza becomes the compass and his opponent's fighting spirit becomes his field of attraction. And as stated by Akaza himself, the stronger his opponent's fighting spirit is, the stronger his Compass / "magnetic field" will respond.

What does a stronger Compass / "magnetic field" do? As explained in the overviews, just as a stronger magnetic field pulls a compass needle with greater force, a stronger Compass Needle increases the speed at which Akaza's attacks drawn toward his target and the force behind that attraction.

So Akaza gets faster attack speed, faster opponent detection and more attack potency to deal more damage to his target.

Now let's look at Rengoku. His fighting spirit is stated by Akaza to have reached the "edge of perfection." To understand how significant that is in terms of quantifiability, replace the word "perfection" with "cliff." If someone is standing at the edge of a cliff, they are not merely close to it but at the absolute boundary before reaching it. There is virtually no meaningful distance left to cover before they fall off that cliff.

Applying that same logic here, "edge of perfection" implies that Rengoku's fighting spirit has reached its very threshold, with only the final step separating him from perfection itself. So in other words, Akaza's statement places Rengoku's fighting spirit as being as close to perfect as one can realistically be without actually attaining perfection.

And so, Akaza Compass Needle / "magnetic field" gets a lot stronger from this against Rengoku, and the rest should speak for itself in your mind after comprehending all of this.

EDIT:

Don't mistake it for me saying that Akaza isn't holding back, that is not at all what I'm saying. I'm just pointing out facts about Akaza's Compass Needle that a lot of you probably didn't know, and then use it to upscale Rengoku.

EDIT 2:

here's a simple analogy to understand it better,

If you pull a door gently, it closes at a normal speed, but if you yank it with much greater force, it closes faster and hits harder. The same logic can be applied here: the stronger the fighting spirit (pull), the faster his attacks are pulled towards the vital points of his opponent and land with greater force via velocity.

ICA Tanjiro was consistently able to defend himself against a serious Akaza by repeatedly blocking and evading his attacks throughout their fight.

There are multiple reasons to conclude that Akaza was serious:

1. In Chapter 67, Akaza states that the next time they meet, he will "spill his brains," while visibly enraged with veins bulging across his body.
2. This attitude remains consistent during their rematch, because in Chapters 147-148, Akaza's facial expressions noticeably change when attacking Tanjiro. He displays visible anger and aggression toward him with veins bulging from parts of his body, whereas his expression against Giyu reverts to his usual excited demeanor when facing a strong opponent he respects.
3. Chapter 149, Tanjiro partially reminds Akaza of his past, which visibly angers him. Akaza calls him "unpleasant" and then aggressively pressures him. This behavior is unusual for someone who normally enjoys battle and takes pleasure in fighting powerful opponents.

Based on this, there is little basis for claiming Akaza was holding back physically. Whether or not he was using his full arsenal of techniques is irrelevant to the point being made. Akaza was clearly more serious against Tanjiro than he was against Rengoku, yet he failed to land a single clean hit on Tanjiro until he resorted to Afterglow, his strongest technique. Rengoku, who is far weaker than this Akaza wouldn't hit Tanjiro either.

Base Giyu scales above this Tanjiro. The two are not truly relative because whenever Tanjiro attempted to assist Giyu against Akaza, he ultimately became a liability, which forced Giyu to save him.

Relativity implies that two characters are comparable enough to consistently compete with and keep up with one another, even if one is somewhat stronger. However, that is not what we see here.

Tanjiro is barely able to keep pace with either Base Giyu or Akaza in direct exchanges, and his attempts to intervene only create openings that Giyu has to cover. This tells us that the gap between them is not small enough to justify relativity.

Put all of this together and you get:

Base Giyu >> ICA Tanjiro > Base Rengoku

That doesn't include STW & SS Tanjiro of course.

Also this is with all due respect to Rengoku because we all love him.

EDIT:
It's funny how the people in the comments disagreeing with this either just say 'Rengoku slams' or bring up completely different arguments that don't actually address or debunk anything I said here. Rengoku glazers are really something else. If you're going to go against what I say, then ACTUALLY make an argument that disproves mine, or else what do you think you're proving?

EDIT 2:
Don't get it twisted, I'm not saying Akaza was necessarily serious against Base Giyu. The point is that Base Giyu scales far above the Tanjiro who was already capable of evading attacks from a serious Akaza, which is already a better feat than anything we saw from Base Rengoku. Throughout the fight, Giyu is consistently portrayed as the stronger fighter. In fact, when Tanjiro tries to assist him, his help ends up accomplishing little to nothing. That is my point.

Sanemi and Obanai both view each other as equals based on the outcome of their sparring sessions.

Meanwhile, not only Sanemi calls Giyu too slow but he also remarks that training with him would make him rusty. So that widens the gap a bit and suggests Sanemi sees a clear difference in their skill levels and places Obanai much closer to himself than Giyu.

Of course, Sanemi's opinion should be taken with some caution since he has a personal dislike for Giyu but I don't think his dislike towards Giyu would change this because he's specifically talking about combat training and evaluating how beneficial a training partner would be, which is apart from the beef they have. If training with Giyu was genuinely as useful as training with Obanai, there would be no reason for him to single Obanai out as the better option.

Tengen VS Shinobu

Let's say that both are at full power and fully intent on killing each other.

How exactly does Tengen win if his best feat is to be relative to Gyutaro (UM6)? The common "counterargument" is that Doma was holding back agaisnt Shinobu. While it is true, people never justify with actual canon evidence that Doma was suppressing himself to such an absurd extent that his performance drops all the way down to the level of Gyutaro (UM6).

Unless someone can provide a solid argument, backed by canon evidence, that Doma was holding back to the point where he would effectively be weaker than Gyutaro, who is an Upper Moon ranked 4 position below him and pushed Tengen to an extreme-difficulty fight, then there is no basis to conclude that Tengen would beat Shinobu.

Understand how proving this point would require nerfing an Upper Moon 2 all the way down to Upper Moon 6 levels solely to maintain the idea that Shinobu is "the weakest Hashira." Thinking about it alone, would make it look far more like an exaggerated interpretation or agenda scaling than something actually supported by the story.

Relativity: Two characters are comparable to each other, but one can still be noticeably stronger or weaker. The gap is small enough that they can compete/keep up with one another.

Pay attention to how they're able to coordinate in combat without one holding the other back. For them to pull off that level of coordinaton, their combat speeds must be within the same general range in scaling.

If one were significantly faster than the other, their teamwork would fall apart, as the slower fighter wouldn't be able to keep pace with the exchanges and just be left behind.

So the fact that they were able to effectively synchronize their attacks is itself evidence that they were relative to each other at that point in the fight.

Yet nobody talks about how this is a big upscale for Yuji, who isn’t even awakened from black flash, yet he’s still able to keep up with Yuta and Rika, whose stats are boosted by his Domain.

They were literally able to coordinate effectively against base Kokushibo, to the point where he was overwhelmed and forced to draw his Long Sword. What he says afterward is also important:

"Once I dispatch you two, the rest will proceed easily."
dispatch: deal with (a task, problem, or opponent) quickly and efficiently.

This makes it clear that his focus had changed toward killing them. If he were truly capable of doing so comfortably without the long sword, there would have been no reason to use it in the first place. He brought it out because he wanted to end the fight as quickly and efficiently as possible.

While yes he may still be holding back overall with the long sword, but that doesn't change the fact that Gyomei and Sanemi pressured him enough to force that escalation, which people seem to overlook. He was barely keeping up with them without LS.

For Gyomei and Sanemi to pull off that level of coordination, their combat speeds must be within the same general range, because if one were significantly faster than the other, their teamwork would fall apart, as the slower fighter wouldn't be able to keep pace with the exchanges. The fact that they were able to synchronize their attacks against Kokushibo is itself evidence that they were relative to each other at that point in the fight.

EDIT:
I am NOT Saying they're equals. Being relative and equal are not the same thing.

Equality: Two characters are on the same level overall, with no gap at all between their stats, or combat effectiveness.

Relativity: Two characters are comparable to each other, but one can still be noticeably stronger or weaker. The gap is small enough that they can compete/keep up with one another.

Gyomei is obviously stronger but it is not by a large margin in terms of combat speed.

Gyutaro wasn't even a blitz tier above a strained EDA Tanjiro, who fought Daki beforehand, because Tanjiro was able to mentally react to him or avoid his attacks on multiple occasions without getting blitzed. And yes, he is still massively weaker than Rengoku, and this should be obvious.

He states that Akaza and Rengoku's movements were too fast for him to follow. The gap there was so large that his perception could not keep up with the fight itself.

If a heavily fatigued EDA Tanjiro can still perceive and react to Gyutaro in combat, then Gyutaro cannot be separated from him by the same kind of speed gap that existed between Tanjiro and Rengoku who literally fought someone three ranks above Gyutaro.

Whether you think Akaza was holding back or not, the fact remains that Tanjiro couldn't even properly follow the fight between them, yet later on is able to perceive, react to, and avoid Gyutaro's attacks while even more weakened shows that the speed gap between Gyutaro and Tanjiro was nowhere near the gap between Tanjiro and Rengoku

Rengoku will blitz Gyutaro to hell and back. Gyutaro's poison won't even become a factor because he is never hitting Rengoku.

To guide your opinion on it:

Being Stronger
is how a character scales overall compared to another character. It is determined by factors such as speed, strength, durability, etc (all existing PHYSICAL stats.) Skill, feats & statements. When powerscaling, the goal is to determine who has the better overall stats or/and portrayal on average.

Knowing this between Kaigaku & Gyutaro would tell us WHO IS THE STANDALONE/TRUE UPPER MOON 6.

Winning A Fight.
However, a weaker character can still beat a stronger one due matchup advantages, like abilities that bypass conventional scaling, intelligence/strategy, environmental factors, mental state, injuries, fatigue, or simply catching their opponent off guard.

To put this in to perspective, if Character A is stronger than Character B in nearly every measurable category, Character A scales above Character B but if Character B possesses a specific ability that counters Character A, Character B may still win but that does not mean he was stronger than Character A.

Basically how much stronger is each Upper Moon than the rank directly beneath them:

• Kokushibo & Doma (UM1 & UM2)
• Doma & Akaza (UM2 & UM3)
• Akaza & Hantengu (Zohakuten) (UM3 & UM4)
• Hantengu (Zohakuten) & Gyokko (UM4 & UM5)
• Gyokko & Kaigaku/Gyutaro/Daki (UM5 & UM6)

Prime Murata victims btw

Stamina and endurance are not the same thing.

Stamina
is how long someone can continuously exert themselves before becoming fatigued

Endurance
is the ability to continue exerting yourself despite physical or mental setbacks, such as injuries, pain, illness, fatigue, or other forms of strain.

In Chapter 154, page 3, it's stated that demons do not feel exhaustion or pain. This would imply they possess infinite stamina, since they never tire. But that doesn't mean they have infinite endurance as well.

Like I said, endurance is normally measured by how well someone continues to perform while dealing with pain, injury, or other impairments. Since demons don't feel pain and are unaffected by exhaustion, they lack the very limitations that endurance is meant to measure, and as a result, their endurance becomes difficult, if not impossible to properly scale.

Humans in Demon Slayer consistently display better endurance feats than demons, yet in WIS edits people still give the endurance category to the demon simply because they assume their endurance scales with stamina. Or is it just a misinterpretation of what endurance actually is?

The only demon with actual endurance feats is drugged Muzan because he was actively getting nerfed to hell and could still handle the verse