In the end, he says, he's just not strong enough to stop the remnant soul from killing him. He blames himself for not being able to protect the world from the evil that's about to happen. He's not the only one who's been transformed into a demon. There's no way he can stop the evil from happening, he tells us, and he can't stop it from happening to anyone else. He tells us that he'll do whatever it takes to keep the world safe, even if it means killing himself.