The protagonist becomes an incubus due to certain circumstances, and in vengeance, he turns his new found erotic powers against a pair of girls that were bullying him.

A former all girl's academy has recently become co-ed, and the few male students that have enrolled will be eligible for a discount on their tuition fees. Due to this, Takeo Hamajima, whose family is poor, decides to enroll..

However, the male students were unaware that the majority of the academy's existing students are opposed to the co-ed transition.

As soon as they enter the academy, they are harassed, bullied, and persecuted by the female students.
One by one, the male students stop attending school or transfer elsewhere.
Finally, Takeo, who has no other choice due to his family's circumstances, is the only male student left...

Day in, day out, he continues to endure a barrage of the harassment.
Then, one day, when he is locked up in the old club wing of the academy by a bully... he finds a mysterious book that will change his life forever.

(Source: DLsite)