Onryo (Revengeful Ghost) (怨霊)

Onryo are common supernatural or ghostly phenomenon that cannot be seen by human eyes that harbor ill will and vengeance towards humans. Due to these attributes, they are classified as evil spirits.

Onryo refers to supernatural phenomenon and the religious idea (in some parts) or spiritual notion that if a person dies in an accident or incident, dispute, suffers punishment or execution, or dies after suffering from excessive mental or physical stress caused by another person, and does not reach heaven or nirvana, but remains in this world saddled with strong feelings (grudges, described below),
the spirit may curse the person who caused their death and in some cases drive that person to death, and in this way seek retaliation.

It is also a term used in storytelling, comics, movies, and dramas and in this kind of fiction the spirits are portrayed as having a physical presence in order to heighten the effectiveness of the story.

Onnen (Grudge)
Onnen indicates a feeling held by a supernatural being that results in a curse that affects another person.

Notable examples
In Japan, examples include the curses of SUGAWARA no Michizane and Emperor Sutoku during the Heian period and during the Edo period Nanboku TSURUYA, the fourth used the 'incident of a wife, Oiwa's murder which in fact happened in the Tamiya fafmily' as a ghost story in his play 'Tokaido Yotsuya Ghost Stories.'

Also, there were also phenomenon reportedly witnessed by an unspecified number of people in connection with onryo ghosts such as the reported happenings in Tokyo during the Meiji Period in connection with the transfer of "a tomb for the head" of TAIRA no Masakado inside an old undisclosed ministry and related curses. However, like with magic, it is impossible to find scientific proof.

Folkloric Background
The usual understanding is that 'there are cases where the place or grave where the person who is said to have became an onryo died, is vandalized or people who merely inadvertently pass such a place become cursed.'

It is said that there have been different viewpoints throughout the ages in Japan and across different regions including that 'the dead become sacred beings', 'the dead become beings to be abhorred' or that 'people who die of unnatural causes become revengeful ghosts and curse the living.'
Some analysis of folklore suggests that 'even during the Edo Period people generally harbored feelings of awe and fear to the dead.'
As can be seen from the above explanation the spirits of the deceased have some ambiguous aspects and in contrast to revengeful ghosts are the ancestral spirits which are honored. Also while not completely unrelated to folklore, the philosopher Takeshi UMEHARA is noted for his work 'History of Onryo' which looks at Japanese history from the point of view of the appeasement of revengeful ghosts.

In Indian Buddhism there are no revengeful ghosts as there are seven opportunities for reincarnation, one each seven days after death, so all the deceased without exception are thought to be reincarnated within 49 days. However in Japan a mixture of Buddhism and Shinto is widespread so some Japanese Buddhist monks and nuns find a source of income in such practices as exorcising spirits. Examples of appearance of onryo prior to the Heian Period include the Hayato burial mound at which it is said the Yamato Government mourned the spirits of the enemy during its conquest of the region.

Deification of onryo
Furthermore, quite a few researchers hold the view that at various shrines and temples, even in the case of historic figures who once lived and are now enshrined (excepting some imperial family members and warriors), 'at first the enshrined people were murdered or died in rebellions and the people were fearful of these people becoming ghosts and placing curses so they deified them.'

In fact, the three greatest onryo and the places at which they are enshrined include: SUGAWARA no Michizane, at Dazaifu Tenmangu Shrine (Dazaifu City, Fukuoka Prefecture) and Kitano Tenmangu Shrine (Kamigyo Ward, Kyoto), TAIRA no Masakado at Tsukudo-jinja Shrine (Chiyoda Ward, Tokyo) and Kanda Myojin Shrine (Chiyoda Ward, Tokyo) and Emperor Sutoku at Shiramine-jingu Shrine (Kamigyo Ward, Kyoto).