>>49939296
Oomukade are only weak to human saliva, which is toxic to them, so semen and the like isn't going to weaken her.
Mythologically speaking, Fujiwara no Hidesato (who Mokou is distantly related to) killed the Oomukade by coating his last arrow in his own spit, which managed to pierce it's armor and poison it.
Concerning Momoyo, most interpretations I've seen either make human saliva weaken her physically, paralyze her, or act as an aphrodisiac. I assume if you inject it directly into her blood or if she overdoses on your spit she's gonna get knocked out.