Arisu is a high school student who faces bullying at school and abuse at home by her uncle. One day, she witnesses her uncle being killed by an assassin called "Arachnid." Thinking that she'll be killed next, Arisu has no choice but to fight back. Soon after, she wakes up at Arachnid's house, and he takes her in as his deadly apprentice.

Nomoto meets a mysterious girl, Hitomi, and gets taken to a junkyard where those with nowhere to go gather. There, a dreadful fighting match called "Killing Bites" is held among "hybrids," beings who have the brains of a human combined with the fangs of a beast...