The Tenacity of a Man and Woman wanting to have a family is an all-powerful thing, one that can't be stopped by anything as mere as Logic! Especially in manga! They will have seggs, they will have children, and they will live a happy life together!They can never have a family.
Probably read “Boku no Kanojo wa Dekkawaii”What should we do now?😥
The ideal ending would have been her gaining the ability to turn giant or normal-sized at willI would have preferred an ending where the giant size was fully embraced rather than handwaved as the result of another "unfulfilled wish"