Since a few in the comments already mentioned Yotsuba's selflessness, I say then it would only make sense that she should be the bride because she will then share her hubby with her thirsty sisters. Harem route preserved, milk'em girls
I thought the knockout blow was Junwoo throwing an elbow. Like others have said, doesn't make sense that a punch would suddenly work by holding your wrist. But turning over your hips while striking someone with a large lump of bone? Night night.