Based on the erotic game by Courreges Ace.

Two high school girls, Chihiro and Eri, were chatting at a hamburger shop after school. As they were talking, Chihiro slowly changed the topic.

"Actually, I want to ask you something... no, I want you to listen to my troubles~"

Chihiro told Eri that sex with her boyfriend is no good, and asked if there is a way to make it better. The experienced prostitute Eri then started talking about her sex experiences and how good it is.

"Right, the customer I had last time was a huge jackpot~! I can't even remember how many times he made me cum~! So, would you like to go and watch us~?"

At first, Chihiro refused the idea, but since she was definitely curious, she finally gave in and said she would just watch them.

(Source: Official Site)