Karas

Humans and demons share the same streets in Shinjuku — except humans have no idea. The demons are invisible, walking right alongside everyone, and the only thing keeping that uneasy peace intact is Yurine and her chosen protector, the Karas. Think of the Karas as a city's immune system given a body and a blade. The problem is, the last Karas went rogue. Eko decided humanity didn't deserve protecting anymore, and now he's building an army of mechanized demons called Mikura to tear that balance apart. Yurine's answer is Otoha, a former yakuza with a messy past and no real reason to play hero. Watching him figure out what it even means to be the Karas — while Eko's forces are already moving — is where the series hooks you. Karas is a 6-episode OVA from Tatsunoko Production, and the animation is genuinely something. It blends 2D and 3D in a way that still holds up, especially during the action sequences, which are fast and brutal. The tone is dark throughout — closer to Darker than Black or Devilman Crybaby than anything lighthearted. If you liked the hidden-world atmosphere of Bleach but want something shorter and more visually aggressive, this fits. It doesn't hold your hand with the lore, so pay attention early. The payoff is worth it.