One night, you were on your way home from work when you met a runaway. With no place to stay, you thought one night would be fine... but the wheels of fate began to go haywire, leading to a life of endless banging.
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're having a hard time getting a girlfriend, so you turn to the local church for some guidance. The nun there decides to give you some confidence... using her own body!