Just about every culture has a history of belief in some sort of supernatural trickster or generally unpleasant or malicious critter. It's easy enough for a person from a western, Judeo-Christian background to call them "demons" but it's not necessarily as clear cut as that in other cultures.
Trickster spirits are not always embodiments of evil, the progeny of some supernatural evil deity, or otherwise naturally opposed to all that is good and right in the world. They are often complex creatures with their own motivations and needs that, while alien to ours and certainly obnoxious and dangerous, aren't "evil" in the strict sense most of us are used to. Examples would be the little people of northern Europe, what you would call elves, faeries, leprechauns and whatnot today although that's not entirely accurate, the coyote and similar spirits in native north American cultures, or many of the Loa of Vodoun tradition.
I don't know if it's fair to just say "they're demons" though because it gives a shallow impression. Er, sorry if that's a tangent.
Anyway I think I'm going to let Miek finish off Yoshine, he obviously has more interest and energy for it. /bow.