Just letting u know, Kousagi's father is actually Mamoru, not Seiya. In a part of Chapter 26, which is before the epilogue, it states that Usagi had actually gotten pregnant by Seiya. she then later had a medical abortion because she didn't want the baby. She then proceeds to attempt to overcome her trauma from the r***, with Mamoru. they then agree on trying for another baby and she ends pregnant with Kousagi. It's not mentioned in the story, I didn't feel like it needed to be, but Chibi-Usa was 5 years old in the epilogue, and Kousagi was around 3 years.