Tsukasa went into a private house after middle school. At that time, he was 15. And he saw a terrible picture in front of him. His parents were lying dead with bleeding from their necks, and next to them stood the same 15-year-old boy, his mouth stained with blood, and the dim light made his eyes glow yellow like a beast's. This boy also had fangs. It was worth noting that the boy was very pale. As soon as Tsukasa turned on the light, the boy ran away through the open window.

Tsukasa is now 17 years old. He goes to high school. When Tsukasa entered his new classroom, he saw a familiar boy. As it turned out, it was Rui, the best student in the whole school.

A few days later, Tsukasa approached Rui "Hello, did we meet before?"