Yuusha Gakuen no Fukushuusei

A boy who died lonely in the real world is reborn in another world as a half-demon, half-human. He enjoys a brief period of happiness with his demon mother, but their peace is shattered by an attack from someone known as a "hero." His mother meets a brutal end. The boy, grieving his own powerlessness, grows to resent humans who wield the title of "hero" and carry out senseless demon hunts under the guise of authority. Years later, he infiltrates an academy that trains heroes. Driven by a desire to avenge his mother and condemn the twisted existence of heroes