I'M QUITTING THE HERO'S PARTY

Raniel Van Trias, the Ashen Wizard, is a highly skilled mage set on defeating the Demon King. After years of fighting alongside the renowned Hero's Party and multiple encounters with the Demon King, he is ousted from the party, left with a curse on his heart, forced to lose half his lifespan, and transformed into a woman! Undeterred, Raniel becomes an assistant professor at the Royal Apelia Academy as Rania and searches for a way to lift the curse, oblivious to how challenging his task may be... (Source: Tapas) — Description from AniList community (anilist.co).