#nagiphobia

The thing is, he exists outside of time and space. But, he can randomly wake up in any Nagisa's body.

Despite his appearance, he's pretty chill?? He just wants to live and experience a regular life (aside from the whole bizarreness of assassination and Korosensei and all that). Whenever he wakes as Nagisa, he goes through the day like any other. He can leave a world whenever he wants, but he can't enter a world on his own, especially without a body, so he takes advantage of moments when he can actually live.

He doesn't stay long though, because 1: he'd basically be stealing a Nagisa's life by possessing him all the time (plus the host is partially conscious but unaware of his surroundings and doesn't realize he's possessed, and isn't that a little terrifying?), and 2: Karma almost always sees right through him. Karma's always been suspicious of Nagisa, especially before the civil war arc, so some Karmas can see through his disguise.

Nagiphobia has two passive abilities: cloak and calm.

With cloak, people only see Nagisa Shiota. The creature acts just like Nagisa (is this creature Nagisa or not, that is the question...), so it's hard to see through the disguise. Even if the creature does something like extend dark claws out of his hands, it'll look like he's wielding knives instead.

But Nagiphobia isn't perfect at acting. People who know Nagisa will realize it's not him, and the cloak will automatically drop to show the shadowy creature. But despite that, Nagiphobia's other ability, calm, kicks in. People feel no danger when they see him. There's absolutely no bloodlust. They perceive him as harmless and unnoticeable, even if they can clearly see him about to attack them (however that may occur).