It was mentioned that females of the Hayase family are the ones tasked to watch Fushi, the mother will try until they have a girl to pass on the job. I don't remember them saying that they kill the male children so maybe they became a branch family or they're abandoned/exiled. I think it was just Kahak who was the only child, since the mother(former chosen) died before there was a girl and apparently there wasn't anyone else suitable/available? That's what I think.
That makes sense
Maybe it took over his dead body and reproduced? Might be why the knocker doesn't have it's original form now, since it tried to survive. Kinda like Parasite, how the guy almost died but the parasite become one with him to survive.
I thought kahak had no kids...... Who's the woman that bore his child.. ? ..... My yaoi ass was rooting for him, lol. Mizuha is just like hayase, so I don't really like her. Kahak is better.....