Maou-sama wa Kaifuku Majutsu wo Kiwametai: Sono Seijo, Sekai Saikyou ni Tsuki

Demon King Ruburuvim lived for over 1,000 years, mastering every possible magical theory. To conquer the one thing he couldn't master in his entire lifetime—Recovery Magic—he has been reincarnated as a young girl!!

It turns out that the key to mastering Recovery Magic is... making friends—!? The former Demon King, a slightly clueless "beginner" at being human, is about to dominate(?) academy life!

(Source: Hifumi Shobo, translated)