User blog comment:IamJakuhoRaikoben/Chapter 497: The Winter Mage, Review./@comment-5303512-20160819011037/@comment-7418318-20160819012057

Your headache is about 10 years late. :P

Except for Rukia, who was adopted into the Kuchiki clan, all the big clans of the Shinigami had only "true born" Shinigami children.

It makes no sense, considering they talk about the balance between living and dead souls, but that's what it is and has been almost since the beginning of the series.