Talk:Re:Zero Light Novel Volume 21/@comment-24727405-20190624134220/@comment-37883549-20190624143336

>They were to be killed as the custom of Oni to protect their pride as strongest of the demi-humans, until just before the execution Ram displayed the potential of her power to protect them both at which shocked the community.

From Rem's page. From that, I can say that Oni's seem pretty clear cut Demi-Humans.