Inugami are dog spirits. Descriptions of their appearance vary greatly. In the most common interpretation, they look like ordinary dogs when they physically manifest near their masters, with their true form being a mummified dog's head. This head is kept hidden in their master's house and is often dressed in ceremonial clothing.

Their are several theories about how an inugami is created, and none of them are pleasant. They often involve ritualistic starvation of dogs, with the exact details varying between stories. Once the dog dies, the person responsible would provide their spirit with food in order to obtain their loyalty. Once bound to their master, who is usually someone from an aristocratic family, inugami will carry out their wishes just like any loyal dog would. They are often used for nefarious purposes such as acting upon their master's grudges against others.

Inugami are loyal to not just their original master but also their family. They are passed down through generations like heirlooms. That being said, they can lose their loyalty to their master if they are severely mistreated. When this happens, the inugami will maul its master to death.

In addition to being able to physically manifest near their master, inugami can also possess people who are emotionally unstable or weak, as well as animals and inanimate objects. Once possessed by an inugami, a person will display intense hunger as well as dog-like behavior.

If the inugami does not leave the person's body, either willingly or via exorcism, the person will eventually die, with their body being covered by tooth marks. If the inugami does leave the person, they will be ostracized as having been tainted by the inugami. For this reason, people who have been possessed by inugami often end up living in isolation.

FUN FACT: Inugami are only found in areas that do not have foxes (inari) as foxes serve as people's familiars in those regions instead.

Examples in various media:

Because of the horrific origins of inugami, depictions of this yōkai often take a lot of creative liberties with them. As such, these examples focus more on the yōkai's loyalty to its master rather than its origins or often malicious actions.

Sadaharu (Gin Tama)

Ranmaru (Kakuriyo no Yadomeshi, titled Kakuriyo: Bed & Breakfast for Spirits in English) He is usually shown in his humanoid form as shown in the second image, although he can be seen in a more traditional dog form as shown in the first.

Inuki (X/1999)