The Blessings of Many Heirs

A delivery guy Haven Ware dies in an accident and wakes up in a strange fantasy world where men are nearly infertile and women wield supernatural powers. Sold into slavery to twin sisters for a hundred copper coins, he discovers their true plan: to have him father a child in place of an aging, barren nobleman. This bizarre mission activates a mysterious "fertility system" that rewards him with power and skills the more affection he earns from the girls.