Living secretly within the human population are two half-bird, half-human species: the cockatrices and the basilisks. Kozakura Sora, a youthful cockatrice, transfers to a new school to fulfill his duty of observing Karasuma Rin, the student council president who happens to be a basilisk. But on his initial day, Sora collides with Rin's younger brother, Karasuma Kai, by accident. This chance encounter is a fateful moment that alters everything.