That's yi yuns sperm dono baby. Do rou rou was Feng fengs sperm but yun raised him, but he still has sperm in there that was replaced with fengs sperm under fengs name. They took the sperm and made a baby because they wanted to hold something against Feng Feng and be like "I HAVE YOUR CHILD YOU HAVE TO GIVE ME ATTENTION NOW" But that's actually Yuns sperm. Remember they switched the names on the sperm cups.
So basically fengs aunt robbed fengs sperm in order to have a baby since she can’t have any naturally but she wanted the baby to have the feng blood however what she doesn’t know is that feng had switched yiyi’s sperm with his (that’s why rourou is fengs and not yiyi) so basically the baby that was born is actually yiyi’s child not fengs
This is so well explain and confusing at the same time.
Yiyi and Feng both applied as sperm donor but for some reason Feng switched Yiyi's sperm with his (probably because Feng knew something like this will happen, his family interfering, stealing, etc.). That is why Rourou is not Yiyi's son but Feng's.
The aunt stole Feng's sperm because she wants to be the one to produce the first child of Rourou's gen = abiding to the family rules about first born being the heirs. However, since the sperm were switched, that newborn this chapter is not Feng's kid but Yiyi's
now im confused...plss fill me up about the latter part of the chap