Cursed Spirits

Kenjaku is father of Chōsō, Esō, and Kechizu.

A long time ago, there was a girl who could give birth to half-humans half-curses. So far it's unknown whether this was simply a cursed technique of hers or if it was some kind of affliction. She had nine pregnancies and each was aborted. Those fetuses were stored at the school and were in a dormant state (until three of them were broken out). I can't recall if "Death Painting Cursed Womb" is a name of the girl's technique or for the fetuses themselves, but that's what it is. Right now those nine are the only known instances of such phenomenon, so it's safe to assume that their mother's ability was either very rare or even the only one of its kind.