https://www.dlsite.com/maniax/work/=/product_id/RJ01492039.html
cover taken from pixiv.

[Synopsis]

One weekend, our protagonist, Kaede Yuzuha, was supposed to be spending his time playing games with his junior as usual.
However, after drinking a mysterious energy drink handed out in front of the station, the protagonist suddenly transforms into a woman.
Though awkward with Yuzuha's new female body, the two find themselves intrigued.
While Yuzuha is in the bathroom, he discovers the pleasure of his clitoris through the touch of his fingers.
While he is masturbating, obsessively touching himself, his junior, Hirai, who is worried that he hasn't come out of the bathroom, finds him.
“Since it happened anyway, why don't we experiment with my female body?”
Hirai, curious about the female body and Yuzuha, eager to discover the pleasure of vaginal sex, begin their intense research into the pleasures of the female body.

Base +28, liberius +6, Tarkov10 +6, Kues +6, Der Fuhrer +13, nuts987 +14