Once, "Integral Sorcerian Academy", which teaches magical experts, experienced an incident called "the night of the red moon", where demons attacked the school.
In order to contain the situation, an all-girl team "Anti-Spectre" was formed by the most prominent students and the demon who led the attack was sealed.
Our protagonist is a freshman who passed the difficult general admission test in order to become a student at this school. He loses his life, while being caught up in the fight between anti-spectres and a demon, but is saved by the sealed demon Morpheris.
The demon's deal in order for the protagonist to live, is to help in breaking her seal and corrupting the anti-spectre team to the pleasures of flesh.
"Next until the moon turns red" is set as a deadline, and if the protagonist fails to accomplish the task, he will lose his life.