他の男の精液を流し込まれるわたし…… 愛する彼女は先輩の肉棒を嬉しそうに咥え込む

The main character, Ryosuke Katase is going to the same school as his girlfriend, Mio Higuchi.
The two spends their days happily together as a couple.

One day, both of them starts to work part time at a cafe where the older Yuichi Takami works. 
Takami is friendly and openhearted toward the all the part time workers except for Ryosuke whom he treats coldly for some reason.

Ryosuke continues to feel uncomfortable but gets the feeling that he himself is not the reason behind it.
It's comforting to know that he has his girlfriend Mio......