Cuddled by a doting big sister who spoils you with whispers and pussy... A naughty big sister who's cared for you since you were both young. A luxurious life enveloped by warm pussy and big tits.
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.
You are under the "curse of lust" that turns women into your sex sl*ves. The only way to break the curse is to cum inside a young nun's pussy..."Please think of me as a tool for your sexual relief and ejaculate..."