@mutsutakashi I don't know if his ability is more overpowered than All fiction, but if he is smart(and willing) enough,
maybe he can kill the possibility of him dying. Maybe kill some memories or existence itself, who knows, his idea of what he can kill is so vague and just get worse when he kills things like items and spells.
I think the only thing restraining him is his beliefs and creativity, haha...