Saigo no Eiyuu ni Sasagu Hanayome Gakuen Toki wo Koeshishi Mahoutsukai, Jidai no Hime to Kizuna wo Musubi Harem wo Kizuku

Alec, the strongest mage, has become so powerful that he finds the peaceful world he created as a hero incredibly boring. Believing he might encounter a worthy rival in the future, Alec decides to sleep for three hundred years… but… When he awakens, Alec finds himself enrolled in what's called...

Source: MyAnimeList