An abnormal phenomenon called “Dark Hour” has been occurring at Jinguu Academy. People who are affected by the “Dark Hour” have their rationality knocked out of their grasp, and they are dominated by their carnal desires.
Tatsuya is a college student and classmate of Saki as well as her lover. However, he has a special “cuckold” fetish, which one day becomes known to Saki. “Are you interested, Taku-kun? I’m going to have sex with other people.”