Mio betrays her boyfriend to be with the senpai she adores... and that one transgression changes her fate.
While on teh phone with senpai f*cking her vigorously Mio tries her hardest to maintain the lie.
Believing he loves her back, Mio also has sex with another classmate at her senpai's request...

Mikoto was threatened with info that could hurt her boyfriend.
She had no choice but to do what the classmate said, and you can imagine...
Defloration in the classroom, exhibition play in the men's toilet, sex training at a love hotel.
How long can Mikoto keep bending to her blackmailer's demands?

[From DLsite English]