Shirota Mahiru (voiced by Takuma Terajima) is an ordinary 15-year-old boy. With a kind personality and a full sense of justice, he is an absolutely upright person in the eyes of his friends. One day, Mahiru met a homeless stray cat on his way home. He took the kitten in and named it Xiaokuro (voiced by Yuki Kaji). Who knew that this action would cause Mahiru to be involved in a century-old struggle between vampires and humans. In an accident, Mahiru signed a contract with Xiaokuro and became Xiaokuro's master. Then, Xiaokuro's vampire brothers appeared one after another beside him. The young-looking and mature Ah Xiu (voiced by Ayumu Murase), the arrogant and venomous Arisuin Misono (voiced by Hiro Shimono), the crazy and radical HYDE (voiced by Ryohei Kimura), and the rude and arbitrary Licht (voiced by Nobunaga Shimazaki), their gathering pushed the wheel of history forward.