I am fascinated by ghosts.  Do you know what Yokai are? 
Yeah! Yokai are actually part of Japanese folklore. 
What do they do in Japanese folklore? 
They were mostly supernatural spirits used in Japanese folklore.
Were they evil spirits or good spirits?
as "supernatural" depends on the time period; but generally, the older the time period, the greater the amount of phenomena that were deemed supernatural in character or cause.
According to Japanese ideas of animism, spirit-like entities called (among other things) "mononoke" were believed to reside in all things. Such spirits possessed emotions and personalities. If the spirit were peaceful, it was a "nigi-mitama", bringing good fortune—such as bountiful harvests. Violent spirits, "ara-
mythical yokai demons, are also associated with will 'o the wisp, with the marriage of two kitsune producing kitsune-bi (狐火), literally meaning 'fox-fire'. These phenomena are described in Shigeru Mizuki's 1985 book "Graphic World of Japanese Phantoms" (妖怪伝 in Japanese).
Folklore Europe.
In European folklore, these lights are believed to be spirits of the dead, fairies, or a variety of other supernatural beings which attempt to lead travelers to their demise. Sometimes the lights are