Celosia Barnes, a troubled human girl who has a habit of dragging herself into violent conflicts moves to the Island of Flamel with her family following a family tragedy.

As Celosia get's accustommed to her new situation, she discovers that the students of her new school, and to an extant, most of Flamel are supernatural in some way and befriends Haruo Machida and his family of kaijus.

The family are in hiding from hunters who see the supernatural, especially kaijus, as beneath humans, forcing the kaijus to fighting back against them.

Finding out their business in not just fighting back against these hunters but to also hunt down the worst of both the supernatural and humanity across Flamel. Celosia joins Haruo and his family's business known as the Hitman Detectives in order to protect her new friends and Flamel from the various threats that threaten both humans and the supernatural.

No matter how much blood is spilled, Celosia and Haruo will ensure that the innocent will live another day.