Saikyou Mahoushi no Inton Keikaku

A young prodigy known as Alus Reigin has defeated more Fiends and reclaimed more territory for humanity than any other living person. At 16, he asks to leave military service, but due to his status as the top Magicmaster in a country with over 100,000 practitioners, he is instead enrolled at a special magical institute. There, he conceals his identity, trains two female Magicmaster students, and continues to fight Fiends in secret.