Yōkai

The common translation for Youkai of demon does little to convey the complex nature of Supernatural beings in both Feudal and Modern Japan.

various translations are: "bewitching apparitions", "apparitions", "spirits", "demons" or "supernatural being which is not a Kami nor a ghost"

Wikipedia notes Youkai as:

Yōkai (妖怪, Yōkai? "apparitions", "spirits", or "demons", also Romanized youkai, yokai, or yookai) are a class of obake, creatures in Japanese folklore ranging from the evil oni to the mischievous kitsune or snow woman Yuki-onna. Some possess part animal and part human features (e.g. Kappa and Tengu). Yōkai generally have a sort of spiritual or supernatural power, and so encounters with human beings tend to be dangerous. Yōkai also have different motives and agendas from human beings, which are often completely incomprehensible. Some modern stories tell of yōkai breeding with human beings to produce hanyō.

Japanese folklorists and historians use yōkai as "supernatural or unaccountable phenomena to their informants". In Edo period, many artists, such as Toriyama Sekien, created a lot of yōkai inspired by folklore or their own ideas, and present day not a few yōkai created by them (e.g. Kameosa and Amikiri, see below) wrongly considered as a legendary origin.

please see SuperNatural Beings of Japan an ongoing work for more details.

Here, we deliberately wil exclude the class of creatures called Tsukumogami, since they are common household items such as candle lanterns, umbrellas, shoes, sandals, scrolls, etc. that have somehow taken on a life of their own - traditionally after having existed for one hundred years. below is a small list of non-human creatures appearing in InuYasha, (excluding Tsukumogami):

Obake:

Oni: Mountain Ogre

Kappa: A Water Demon with webbed hands and feet, a turtle shell, and a circular sih on top of its head. It can exist out of water only as long as the dish contains water.

Kitsune: Fox Demon. most often appears as a woman to human men or as a man to human women.Often wishes to merely play pranks, but sometimes desires to amte with humans. The famous Shinto onmyuji Abe no Seimei was said to have had a human father and a Kitsune mother. Shippo is a young Kitsune. Tanuki: racoon dog youkai; Miroku's companion

Tengu: a mountain spirit with a beak and