That doesn’t work for me because even if the MC isn’t sterile, the superhuman girls will be, and there are several that are, and I like them.
They aren't sterile, their genetics are changed so much by their monster parent that normally they wouldn't be able to have kids. But the MC should be able change their sperm's genetics to fit who ever they want.
Even if they were sterile in the traditional sense when they were human becoming a superhuman would fix that.