Yui and Kou have been childhood friends for longer than anyone can remember. As they became adults they also became lovers.
They couldn't keep their hands off of each other, having sex in just about any place imaginable, including at school.
Unfortunately for them, the person in charge of the school cameras decided to blackmail them.
Now Yui has no option other than to obey her teacher or he will let the videos go viral.
However, she slowly becomes addicted to her teacher. -MyAnimeList