The setting is a "delivery health" (dispatch brothel) service where all the girls are from "Isekai" (other worlds), and it would seem that semen is the only source for replenishing their mana in this world.
Imagine a late-night church where a donation gets you nun handjobs, titjobs, virginity-shedding raw sex, and even anal! Hallelujah! You'll certainly be back for service again tomorrow...
Yunon, a JK girl, calls out to you on the train station platform…She'll mock you for being a virgin as she helps you lose it in the bathroom! She'll rile you up as she blows you, lets you finger her, and then lets you put it in!
You're in the car with your girlfriend, Iyu, after your date... As you give her a goodbye kiss, her horny switch gets flipped on! Going to a hotel would take too long, so you decide to do it in the car...
As a male prostitute, you are bought by a succubus disguised as a nun. She is a closet pervert, and she will fuck you silly... So silly that your sexual tastes may end up changing.