Read manga: If I Don’T Die Soon, I’Ll Become The Ruler Of The Demon Realm!

manga
Summary:

Humanity’s strongest warrior was killed by demons amidst a battle and gained the power to reincarnate, but somehow did so as a demon. Only by dying he can go back to living as a human, so he committed suicide non-stop. But things turned out to be the opposite of what he expected…