The cold-blooded Demon King who has beaten all his enemies, who has always been second to none, ended up losing all his magical powers to a female hero who hexed him. What is this magical ritual that you do with the opposite sex’s lips? I can’t believe that even I, the formidable Demon King, have been defeated by this mysterious move! But no worries, I can retrain my abilities. It doesn't matter if you’re a succubus, an elf, a beast woman, or a noble hero’s descendant. I’ll use you as my training partner if I can help it. In order to revive the demon race, I’ll show you the Dual Cultivation Method!

Original Webtoon
Official Japanese

The cold-blooded Demon King, unparalleled under the heavens, lost all his abilities to a crude trick by a female Hero. What is this magic ritual that requires you to give mouth to mouth with a person of the opposite sex? Even I, the Demon King was bested by this oddly suspicious attack?! But no worries, I can always regain my abilities. Even if you’re a succubus, an elf, a beastwomen or the noble hero’s descendant. As long as I can use you to further my cultivation, I will. In order to revive the glory of the Demon Race, this magic called the “Cultivation of Yin and Yang”, I’ll learnt it and show you!