Sefure no Senpai THE ANIMATION

Yuuma attends a freshman welcome party hoping to score at his university debut. Suddenly, Nana-senpai, who is looking for a casual sex partner, asks to go back to Yuuma's house!? This senpai, who was incredibly popular at the welcome party, is now coming to back his house and wants to have sex…? As soon as they enter the front door, Nana-senpai begins to gently stroke his erection… Confused, Yuuma lets her do as she pleases and winds up losing his virginity...!?

(Source: PinkPineapple, translated)