Oni

 Oni  (Oni, 鬼) is a race of powerful beings who are in constant conflict with humanity, seeing it as their natural enemy and vise versa.

Appearance
Ogres (Oni in Japanese) have quite a few similarities with the demons, but are actually a different race. According to Mikoto their horns are considered a proof of them being such. It is also revealed that while most of the Ogres take on a humanoid form there are also special cases which can manifest themselves in objects.