Naoya Zen'in: How to Write A VILLAIN
Art is by Kan (kankan33333).
(disclaimer: i don't condone or agree with naoya's personality or his actions, i just think he has layers to his character that make him really interesting as a character and not too many people talk about it)
First off, his upbringing. He was raised into a patriarchal and sexist clan that viewed women as inferior in every aspect. This must have really been hammered into him as a kid, cuz his sexism compared to everyone else's in the Zen'in clan is insane. (Then again, we don't see too much of them.)
Then, he hears about Mr. Parlay himself, Toji. He's quick to assume that he's pathetic and weak because of his Heavenly Restriction and having no cursed energy, but his mind was completely changed when he actually sees him. He idolizes Toji because he shattered his whole worldview on what it means to be strong. People without cursed energy have no place being sorcerers, yet here's Jujutsu's Greatest Failure, making a whole clan shit bricks with just his name. He hates his brothers and views everyone in his clan as weak because in his eyes, they're blind to what strength is. They're too "weak" to acknowledge the strong. And only he could stand with him (and Gojo) because he's the only one that saw and acknowledged Toji's strength when no one else could.
Then, the way he fights Choso (and initially, M*ki.) He was constantly showing off and flexing, letting his opponent know that they ain't shit, yet he keeps that same energy in every fight, regardless of how bad he gets his ass whooped after the fact. His overconfidence makes him blind to the truth and fucking stupid, ironically exactly like how he viewed the Zen'in clan for rejecting Toji. It's also a parallel to his raging misogyny running rampant even after getting skull-fucked by M*ki. He views women as weak, useless, the whole nine yards, yet he still has the same views and doesn't change any of his thoughts, all while his face is caved the fuck in. He's blind to the truth of the strength women are capable of because of how he was raised and how he lived his life, exactly like, once again, the Zen'ins with Toji. They refused to acknowledge Toji and his strength because it went against everything the clan stood for.
(I also wouldn't be surprised if Naoya modeled his style of fighting after what he imagined Toji's would look like. He idolizes him to such an insane degree that I wouldn't put it past him to do something like this.)
I think this also plays seriously into Naoya's hate for M*ki, especially during their fight. He sees M*ki with Heavenly Restriction and her fighting style, and views it not as an insult to him perse, but more so as an insult to Toji, the one he admires the most. It also adds a layer of irony that Naoya probably decided to mold his style of fighting after what he imagined what Toji's would be like, yet M*ki is able to fight like a 1-to-1 copy of him, though Naoya didn't know it. It's also funny how he thinks people who fight with weapons are lame and makes them bitches, yet the person he idolizes fought almost exclusively with cursed tools.
This is all made worse in Naoya's eyes because of M*ki being a woman. He sees the legacy of Toji being squandered and spit on by M*ki just because of her gender, not realizing she's actually doing what Toji always dreamed of doing. He thinks women are incapable of being strong; hell, he doesn't even give them basic human decency or respect, yet here's M*ki, giving his brothers and the Hei PTSD because of how she was like Toji brought back to life. They saw the Greatest Failure reincarnated, brought back from the dead to lay waste to the ones who rejected him.
Also the fact that Mai, the woman Naoya said was essentially "one of the good ones", was the same one that gave M*ki the strength to destroy the clan and beat the shit out of him was incredible. And his death was done amazingly. One of the first things we hear him say is "Any woman that can't walk at least three steps behind her man deserves to be stabbed in the back and killed." And guess how he died? A woman, taking three steps behind him, stabbing him in the back, and taking his life. Absolute chef's kiss in writing and characterization. Honestly, the main reason Naoya works so well is because of how he's a foil to M*ki. His character would just not hit the same if he was the villain for any other character in the series.
I'm not gonna get into the manga spoilers and what happens there, but in my opinion it just elevates Naoya's character even more, plus it gives him one of the coolest cursed spirit designs in the whole series. He's a piece of shit, but he's a well-written one. And also he has one of the coolest cursed techniques, and the way his fighting style is adapted in the anime made him one of my favorite characters. He's a perfect villain for M*ki, and one of the best villains in the series in my opinion. He and the Zen'in in general are a great take on the classic tale of "those who don't learn from history are doomed to repeat it", and I think it's done masterfully.
Well, that was a lot longer than I thought it would be LMAO. But I hope you enjoyed my little analysis. This is just my take, but I still wanted to share it. Any extra thoughts you wanna add to this is welcome.