Kougekiryoku Zero kara Hajimeru Kenseitan

Eugene Santafield is a young man who dreams of becoming a magic swordsman. There's only one problem, though—he can't use any attack magic! As if in exchange, the goddess of fate blessed him with extremely powerful defensive and healing magic, but he still has to endure the mockery of his peers for his lack of attack skill. After fleeing to the Lykeion Magical Academy to escape from those who know of his failings, he meets the Fallen Queen Erinyes, a Demon Queen who once ruled over the land. Erinyes, taken with Eugene's potential, appoints him to be her caretaker. In addition, the headmaster of the academy assigns Eugene to be the guardian to Sumire, a mysterious outworlder who's really an Ifrit of legend. With these two women at his side, the weakest magic sword wielder is sure to become a legendary swordsman...right? (Source: J-Novel Club)