User is Dazai

Corruption.

The name of Chuuya's ability.

He can't use it by himself, because he can't control it.

That's why Dazai, is the one who helps him. That's why they became partners in crime.

But... Chuuya's ability was slowly killing him.

Slowly and silently.

Dazai started to notice that Chuuya was coughing too much lately. But he always says that he's okay.

But Dazai doesn't believe him.

One day, Dazai caught Chuuya in the bathroom coughing blood.