
Its like this...
They put somekind of spell to him so he can't say he have yang obstruction and give him a pil thats why he got pregnant (this is just my own teory, i dont know if its true or not we still need to see), but if its true that they already plan all of it... Then the body they want is their child cause the healer said their child will be much more stronger
Just a teory... So idk if its will happen or not

I think the theory about Yang obstruction is likely. But the pill that got him pregnant is the golden toad pill or sth that Yuhwa (the woman with yin obstruction) fed him that caused him to lose his pube lol. It was confirmed by the healer grandma.
My theory is, they want Soun's body as a vessel. It's either using white haired dude before the fight or after he lost the fight.
Dont tell me soun is planning to sacrifice himself (unconsciously?)cuz he knows he is gonna die anyways or something like that