The Japanese term for a ghost or spirit driven by intense emotional attachment, especially vengeance, is onryō.
Onryō are spirits of the dead whose anger, grief, jealousy, or desire for revenge is believed to affect the living. In traditional stories, their unresolved emotions can cause illness, disasters, or other misfortune. The concept reflects a recurring Japanese folklore theme: improper death or neglected remembrance can disturb relations between the living and the dead.
A famous historical example is Taira no Masakado, whose spirit was feared after his rebellion and death in the tenth century. Shrines and rituals connected with such figures could help appease or honor them. The practice illustrates how fear and reverence sometimes overlap in Japanese religious history.
Onryō are a type of yūrei, the broader term for a ghost or spirit of the dead. They are also different from kami, although a powerful or dangerous spirit might later receive shrine worship and become part of a kami tradition.