Papa, Akachan Hoshii

In a future where same-sex couples can give birth to their own babies, a son begs his foster father to make one with him.

A man has been raising his nephew for 14 years, ever since his sister and her husband passed away in an accident. His "son" has finally grown up into a wonderful young man, and now, he's seeking to fill his carnal desires... with his foster father...

(Source: Renta!)