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? 
Every spirit was different. There were good spirits, called nigi-mitama and violent spirits, called ara-mitama. 
Were the two different spirits at war with each other? 
I'm actually not sure, but some ancestors could be considered nigi-mitama, giving them the status of protective gods.
They looked over people? 
Yeah! Sort of like a guardian. Certain animals could be either nigi-mitama or ara-mitama as well. It just depended on the area.