WHAT???

Ok so basically that kid isn’t auties child, it’s actually Yiyi’s bcuz she took his frozen sperm. They can’t give him an after birth name bcuz before birth Rourou named him Big Head, hence the grandpa saying to find the original name giver to give the babies after birth name
Lol hope that clears it up a bit

Spoilerrrrr....
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I hope this is accurate, we know Rourou is not Yiyi's actual kid. Yiyi's sperm was swapped out with feng's So the aunt wanted to steal feng's sperm so that the kid would have the blood of the family line and use it to her advantage. But in reality the sperm they used was Yiyi's. The aunt brought big head to the grandfather so that he can finally be named and be recognized as a family member. So the grandfather realized Bighead isn't apart of their family and that he wasn't originally suppose to be born. Now he wants to find the person who can change fate.