There’s the mc, the mc’s dad, and the mc’s stepmom. The dad runs a clinic and the stepmom is a nurse (I think). They want their own child but the dad doesn’t have viable sperm anymore so they both ask the mc for help by having him impregnate the stepmom. Mc is reluctant (at first) but agrees and has sex with her again and again in the clinic and she gets impregnated. Later, his dad comes back and congratulates and thanks his son. The mc’s dad and the stepmom then are really excited to raise their future child.