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The story is this boy is a servant in an influential house.
He has a crush on the daughter of the house. She ends up marrying someone else but they have fertility problems. Her husband then has her and the servant sleep to produce an heir ( it was a pretty good 3some) She does get pregnant and in the last chapter the child accidentally runs into the servant and you can see them interacting as servant and young master. It's only a couple chapters but the art was really good.