I've been trying to put together some stuff for a new OK KO AU I want to come to fruition. But the thing about that is: it's an AU that's more on the darker side.

Now quick warning before I go on: one of the details involves the unfortunate death of a significant character from the original show! Keep that in mind!

Now then.

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Here's some things that I have figured out so far:

• It heavily involves a devasting demonic invasion turned apocalypse.
• One of those demonic entities ends up killing Carol. Right when KO is physically around. In cold blood. This ends up being very traumatic and devastating for him.
• Feeling utterly helpless that he was unable to prevent her death he basically takes this loss extremely hard, grieving her.
• He desperately tries waking her up but literally nothing works
• He cries his eyes out after he processed what happened
• He makes a vow of revenge against that very demon (and technically in a way, others of the same type of demonic creature as that one)
• He also makes this vow to take lives of people that are truly horrible in nature, people that he believes are truly deserving of death; that are irredeemable... after something supernatural happens to him that makes him partial demon/human and gets demon powers
• He becomes some sort of self-appointed vigilante
• Also after these events happening it goes on for a couple more years, leading to KO being in his teens in present day.
• Currently in present day, besides KO, out of the hero side, Elodie, Enid and Dendy are alive.
• Lord Boxman is still alive... somehow.

Things that I haven't figured out just yet and need help with it:

• How the invasion/apocalypse even starts in the first place.
• Who or what caused it.
• I know I want the demonic creatures to have monstrous forms/designs, but I have no idea what their demonic race name should be...
• I don't know how to lead that specific demon to killing Carol in the first place.
• There's a thing I wanna do where a good, significant portion of people on Earth get infected with whatever demon stuff and lose completely who they are as themselves and instead become their malevolent, corrupted demon pawn, but how exactly? (besides people dying and getting killed by them too, that part I know)
• I'm trying to have ideas of something that happens to POINT, but I dunno what. Are they dead? Alive? I don't know!
• I am stumped on how KO becomes this half demonic self-appointed vigilante executor person.
• Also, I'm thinking of adding a small amount of angel... or deity kinda thing in the mix, but I'm not sure how or even what to do... should I even do that? Would it be appropriate??

I do, at least, have an AU name I came up with that sounds pretty good to me:

Vigilante from the Depths

so guys, help me out here, I need ideas to actually solidify this and put it together to be AU ready. WhadoIdo??