Shaped by experiences that left him weary of human relationships, Rei Hitoma openly dislikes people. Seeking a quiet, uneventful life, he accepts a teaching position at a secluded school in the mountains, only to discover that his classroom is anything but ordinary. The students under his care are demi-humans who have gathered there with a singular goal: to learn what it means to become human.

Despite his disillusionment, Rei finds himself responsible for explaining human behavior and social norms to mermaids, bunnies, werewolves, and the like. As his students earnestly struggle to understand humanity, their questions and aspirations gradually expose the contradictions in Rei's own beliefs.