Hanaori-san wa Tensei Shite mo Kenka ga Shitai English Subbed

Once the Demon King, now a shut-in NEET—Ryuusei Narukami’s second life is anything but peaceful! When Meteor Hanaori, the Hero who once defeated him, suddenly returns as a normal high school girl, his world is thrown into chaos. Determined to change, Ryuusei reenters society as a teacher and ends up teaching at her school! Their explosive reunion reignites the past—and sparks an unexpected love!

(Source: Crunchyroll)