WMG / Ao Oni

The Ao Oni are completely sensible, even benevolent creatures, however...
The scent of humans drives them mad. They lose all control of themselves and can't help but chase them down.
  • Crom Oni, while a fan made game does have a group of Oni's that are completely civil, friendly, and passive. They even play let you play a minigame if you have the Kitchen Gun.

The Ao Oni is the creation of human suffering
Wandering around the house, you find prison cells, and even later a strange altar and weird hospital beds. What if some family had a deformed baby, and they kept the baby hidden from the world, and imprisoned it as it got stronger and stronger. The fact that dead things in the house become Ao Onis as well is because of all the suffering the main Oni went through, which turned it from just a weird defect into a supernatural monster.

The Oni are creations of Tommy Wiseau.

The Oni evolve.
  • When your friends change, they turn into a being that looks like the original monster, but with their hair. Takuro keeps his human for a while and only changes when you go into your menu. Other versions of the monsters are deformed beyond recognition of humanity. Now, unless they are demons or perversions of other animals, maybe the longer a human is an Ao Oni, maybe the more their body mutates.

The Ao Oni remember their pasts.

The Ao Oni can choose their form.
  • This goes with the evolution and the "remembers their pasts" theories above. Maybe the Ao Oni are sapient enough to choose their form. Takuro looked human, but obviously wasn't. Maybe they learn to control their bodies and can eventually turn into other forms like the ones locked up in the basement.

The Ao Oni are the earliest Titans.
Think about it. They are big but not too big and we see humans turn into them when they die.