https://www.dlsite.com/maniax/work/=/product_id/RJ01455454.html

[Synopsis]

One day, while the protagonist, "Kohai-kun," and his fellow slacker, a long -haired, black-haired high school girl named "Downer-senpai" are slacking off together in the gym storage room,
she suddenly approaches him with a horny, female-like expression, pretending to be a slut...
Downer-senpai's true nature is that of a low-pressure and extremely perverted girl.
He is seduced one-sidedly and intensely with a passionate blowjob, anal licking and has raw sex with Downer-senpai.

Base +28, nuts987 +14