Houkago no Senpai

Storyline

Masaya loves Mayumi, who is one year older than him. However, he can't tell her that he loves her. One day, he tells Sayoko, who is his childhood friend and one year older than him as well, about it. She promises to help him and starts taking her clothes off.... "I'll give you a sex lesson just in case, right?"

Source: IGDB