After all these years of Katsuki attempting to become a great hero, he failed. And along that, he also lost his mind. He did the only thing that he could and joined the league of villains, officially becoming a villain. He usually used his explosions to kill others, but when he didn't want to get caught and deal with stuff, then he simply used a knife, not to attract people's attention. And the day you caught him, he became even more insane.