Responses
From what I understood, no Yiyi didn't give birth. He flew to the US to do a procedure to put his sperm into a 'surrogate' mother. This unknown lady give birth to Rourou. However, Yiyi's sperm was swapped by the...brown hair guy. Hence, Rourou is the brown hair guy's biological father. I think this probably explains why Rourou has blond hair, his biological mother has blond hair.
I think you replied to the wrong comment
This whole mahua is actually just so fricking cute&funny I love itttt sjbsbs