The Magician's Academy

Takuto Hasegawa attends a magic academy that appears on no map. During a summoning exam, he makes an error and produces a girl named Tanarotte — an accidental creation who possesses enough raw magical power to destroy the country but has decided to follow Takuto with absolute loyalty. The academy exists in a universe where three worlds coexist — Heaven, the Human World, and the Demon Realm — and where both gods and demons maintain a careful pretense of non-existence, largely so they can keep importing human goods that have become coveted commodities in both their realms.