Because the other Races were sealed away the concept of Hybrids was never a thing until reality was rewritten and Rinne met Kai after all Rinne is a prime example of both a Hybrid race and the mythic beast known as the Chimera
Comment by Sandstone on Naze Boku no Sekai wo Daremo Oboeteinai no ka? - Chapter 36.1
2 Replies
@Sandstone or she is a goddess and the races were born from her
@Lorddoug it actually makes some good sense