Ghost

are spirits of the dead in Japan who have been kept from a peaceful afterlife for various reasons and are now cursed to haunt the living.

According to Japanese belief, when a person dies their soul passes on to a heavenly afterlife, which is accomplished through a number of funeral and post-funeral rites and prayers performed by their loved ones over many years. Through these rites, the soul is reunited with its ancestors and becomes a family guardian spirit which are enshrined in the house and continue to be honored as members of the family. Souls that do not receive the proper funeral rites cannot pass on. In addition, those who die suddenly, tragically, violently, or with a grudge and malice in their hearts are sometimes also unable to pass on even with the proper prayers and rites. These souls remain stuck within the realm of the living and are considered "Yūrei".

As restless spirits, Yūrei are stuck in the realm of the living until someone can put them to "rest". Until then, they tend to haunt a particular place or person that has meaning to them (eg. the place where they died or are buried, their killer, or their loved ones).

Appearance
There are many different types of Yūrei, whose appearances and behaviors differ depending on the circumstances surrounding their deaths. In most cases, though, Yūrei appear much like they did in life, retaining the features and the clothing they wore when they died or were buried. As a type of spirit, they generally appear translucent and even then are only very faintly visible, so much so that they appear to have no feet.

List of Yurei in Negima! Magister Negi Magi

 * Sayo Aisaka: a friendly Yūrei who died at the age of 15 while tragically protecting her sister's garden during a storm. For 60 years she was stuck haunting the Mahora Junior High School, particularly Class 3-A, until she gained a friend in Kazumi Asakura and became "attached" to her.

Love Hina

 * In the anime of Love Hina, Motoko is assigned to investigate and exorcise the of a woman who, after being betrayed by one man after another, threw herself into the ocean and returned to exact her wrath upon all men. Able to take possession of women through cursed jewelry, Motoko was able to exorcise the ghost through the use of the Rock Splitting Spirit Sword technique.
 * The mother of Haruka Urashima,, used to look after the residents in the Hinata House's annex as well as running the Hinata Café. Soon after giving birth to Haruka, however, she fell ill and passed away. Yoko's spirit now resides within the Abandoned Annex where she used to look after the ill. When he was four years old, once wondered into the Annex and encountered Yoko's ghost; although at the time he mistook her for Haruka. They would meet again years later when he and the Hinata residents were trying to stop a group of treasure hunters; resulting in Yoko personally appearing to save them.

UQ Holder!

 * is an Onryō who was initially a Toire no Hanako who befriended until he was killed by a group of bullies he attempted to stand up against. Tired of the unjustified caste-system that had developed after the revelation of magic, Sayoko opened herself to the vengeful spirits of all those who had been unjustly murdered or otherwise oppressed by the living and became an Onryō bent on humanity's destruction; unleashing a zombie apocalypse upon the Earth that was only stopped by Santa's intervention.

Trivia

 * Yūrei are frequently depicted being accompanied by a pair of floating flames or will o' the wisps (also known as "Hitodama"). These flames are separate parts of the ghost rather than independent spirits.
 * While all Japanese ghosts are called Yūrei, there are several specific types of Yurei that are classified mainly by the manner they died or their reason for returning to Earth.
 * Onryō: Ghosts of people who died with such strong passions –jealousy, rage, or hatred – that their soul is unable to pass on, and instead transforms into a powerful spirit of wrath who seeks vengeance on any and everything it encounters. They are often victims of war, catastrophe, betrayal, murder, or suicide and are the most dreaded of the Yūrei.
 * Goryō: A type of Onryō that targets the Japanese aristocratic class.
 * Ubume: A mother ghost who died in childbirth, or died leaving young children behind. This yūrei returns to care for her children, often bringing them sweets.
 * Funa-yūrei: The ghosts of those who died at sea. These ghosts are sometimes depicted as scaly fish-like humanoids and some may even have a form similar to that of a mermaid or merman.
 * Shiryō: Ghosts who return to their loved ones for the purpose of taking them with them to the afterlife.
 * Zashiki-warashi: The ghosts of children that reside within a tatami room known as a "Zachiki". Often mischievous rather than dangerous, they are believed to bring great fortune and riches to those whose houses they haunt and will bring about a household's downfall if they leave.
 * Chōpirako: A greater type of Zashiki-warashi.
 * Usu-tsuki-warashi: A lesser type of Zashiki-warashi. They are usually the spirits of children who were killed so that the rest of the family may eat; a common practice during times when food was scarce.
 * Makura-gaeshi: A child ghost who dresses as a Niō, a monk, or a samurai, and appears in bedrooms late at night to cause mischief such as flipping pillows from one end of the bed to the other.
 * Toire no Hanako: A type of meek Yurei who tends to haunt school bathrooms.
 * Putting a Yūrei to "rest" varies depending on the reason the spirit has become stuck; some might require that their killers be brought to justice, their lost bodies being found, or to have a message passed to a loved one. Some Yūrei might just be reluctant to accept their deaths, whereupon an exorcism performed by a priest may be required.
 * Sometimes the only way to end a Yūrei's wrath was to transform them into peaceful, benevolent spirits. This was done with the help of Priests and Onmyōji, through the religion known as Goryō Shinkō (the religion of ghosts).
 * During the summer holiday of Obon, the spiritual world, particularly family guardian spirits, are said to return to the material world to be with their families.