User blog comment:Rei Furuya/Death of a Demon/@comment-36009152-20181110160933

Very good question, Demons are kind of a spirit/thought in a way. Can a thought even be killed?

I guess thinking logically they could be banished; perhaps the weapon they inhabit could break/shatter to symbolize their end. Even after that, they could still occupy their own plane of existence if you like.

Seraph of the End has it’s own very good take on Vampires, Seraphs and Demons so it could be anything. That’s even if they can be killed in the traditional sense. Again it’s conjecture but killing them isn’t even the approach, it’s keeping them under control to use their power, or finding a way to sever the link to be rid of them, if you wanted to.

If it were to happen, the immediate effect is the huge loss of power for the human, and anything could happen to the demon themselves and the weapon.