Protagonist Marusawa Itsuki annoyed by living thing of tentacle parasitic inside of the body. However she the living thing is shared with a part of the spirit and it comes to coexist.

Then, Shinjou Rui that appears for the sake of the living thing of the tentacle exterminating and it combats, Itsuki that wins barely. According to Rui, the mysterious, continuous disappearance event occurs recently, the living thing of the tentacle seems to be discovered from the victim's body.

Faint curiosity and the sense of justice in the heart of Itsuki that hears the talk, complex feelings of revenge heart to the mastermind of the event begin to bud. And, she the ability obtained because of coexistence with the living thing of the tentacle is used, the decision to cooperate in the investigation of the event was made...

Early summer a season to travel and Itsuki reconsider that disgusting case. In the distinguished family girls school with the school tradition with good intentions to accept the student who doesn't have the relative, Itsuki that obtained information that disappearance event occurs. The woman who sneaks as a student, similarly the investigation of the school is started with Rui that sneaks as a teacher.

Itsuki with the core of the disappearance event, can the truth of the living thing of the tentacle be obtained...