|“||Katashi: "This is Japanese kanji for "self." This means he is still himself. The Oni are looking for one who is no longer themselves."
Allison: "What do you mean, no longer themselves?"
Katashi: "Possessed... by a dark spirit. [...]"
Argent: "The Kumicho."
Katashi: "That's right. He was possessed by a nogitsune. It's what helped him rise through the ranks of our Yakuza family."
Possession is the supernatural ability for a spiritual being to take over an another being's physical body. The act usually results in the host's mind being totally subsumed by the spirit possessing it, but this is not always the case. Only two known species have been known to possess others, and a third has shown a very rare potential to possess another, or at least control them with their spirit.
Known Users of Possession
Spiritual Kitsune such as the Nogitsune are capable of possessing a host—this typically means an alive human host, but Kitsune have also been known to possess the dead as well (as evidenced when the Nogitsune possessed Corporal Rhys' corpse). Most of the time, the Kitsune spirit completely takes over its host, but in one known instance, a member of the Japanese Yakuza mob in the 1980s seemingly voluntarily allowed himself to be possessed by a Void Kitsune in order to rise through the ranks of their mafia-like family, eventually becoming the Kumicho, or leader, in the process; this seems to imply that the Kumicho and the nogitsune possessing him had an arrangement to share control over his body.
In other cases, the Kitsune may need to gain more strength before it can exert its will through the body they have possessed. In the case of the Nogitsune who possessed Stiles Stilinski, the Void Kitsune had been imprisoned within the roots of the Nemeton for the better part of a century, requiring an external foxfire source to trigger the Nogitsune's power within him; it wasn't until he manipulated the Thunder Kitsune Kira Yukimura to inadvertently electrocute Stiles that he was able to start controlling him.
Even then, if the vessel has an especially strong sense of will, the two spirits may fight each other for control, with the Kitsune potentially needing to use other methods to regain control, such as blackmail or threatening of the vessel's loved ones. The Nogitsune possessing Stiles threatened to kill everyone Stiles knew and loved if he didn't "let him in," which worked on two separate occasions. However, there are other ways to weaken the spirits possessing these other beings, such as using letharia vulpina, also known as "wolf lichen," a poison used against canine species (such as foxes, coyotes, and wolves (and their supernatural counterparts Kitsune, Werecoyotes and Werewolves) to suppress the spirit and allow the body's true inhabitant to take back control.
Hellhounds, spiritual canine shapeshifters who ride with the Ghost Riders of the Wild Hunt, possess the bodies of humans on earth in order to fulfill their missions as guardians of the supernatural. Unlike those possessed by spiritual Kitsune, Hellhounds are generally more benevolent in comparison due to the fact that they try to remain neutral while completing their tasks.
For Jordan Parrish, this meant he was possessed just as he himself was about to die in an IED attack while on tour with the United States Army Corps in Afghanistan; at first, he was almost completely unaware of his new supernatural status until the Dread Doctors appeared in Beacon Hills, which caused Cerberus, the Hellhound spirit possessing him, to take over his body at night to protect the secret of the supernatural by disposing of the bodies of the Doctors' failed Chimera experiments. This then developed until Jordan and Cerberus came to an agreement to share Jordan's body and Cerberus' powers so that they were in balance, allowing them to become more powerful as one entity in order to help the McCall Pack defeat the resurrected Beast of Gevaudan. However, even when Jordan and Cerberus' spirits were not in sync, Jordan still had access to some of his powers as a self-defense mechanism, such as his immunity to fire and his superhuman strength.
Another Hellhound, Halwyn, possessed a human man at some point prior to the turn of the 20th century in order to defeat and imprison the Anuk-ite, an ancient and powerful shapeshifter, within the Wild Hunt's dimension. It is unknown if Halwyn is the name of the Hellhound spirit or of the human it possessed, but it survived for nearly a century in his vessel, due at least in part to the fact that it entered a hibernation-like state through being placed in a freezer cell at Eichen House. Given how much control and experience Halwyn had with regards to his powers, the Hellhound spirit seems to have either completely subsumed the spirit of its human host, or the two spirits came to a similar agreement to that which Jordan and Cerberus made in order to become one entity and share their respective gifts.
For those vessels who have not yet found a state of balance between their human and supernatural spirits, extreme temperatures have been shown to force a transformation between their respective states; for example, exposing Jordan Parrish to fire caused his Hellhound powers and personality to come out, and putting him in a freezer unit allowed him to enter a trance-like state with which the Hellhound possessing him, Cerberus, could be talked to outside of its normal active hours. It has also been implied that Hellhounds are naturally nocturnal creatures, and, in vessels who have not reached an agreement to balance each other, the Hellhound spirit would typically stay dormant during the day and would then become active while the human spirit slept after nightfall.
Though Werewolves as a species do not possess the power to possess others, there have been two known Werewolves who have achieved a possession-like state in the body of another due to external means.
The first case was with Peter Hale, who, during his brief stint as an Alpha, viciously attacked and gave Lydia Martin the Bite; though he initially made it seem as though he simply wanted Lydia as a third Beta, he later revealed that he bit her so that his spirit would be bound to her in the case of his death, a circumstance that was likely possible due to Lydia's latent Banshee heritage. After he was, in fact, killed by his nephew Derek Hale, Peter's spirit attached himself somehow to Lydia's mind, allowing him to influence her thoughts and actions through hallucinations and dreams until he was able to use her body to resurrect himself on the Worm Moon through a mysterious ritual.
The second case involved the infamous Beast of Gevaudan, whose true name, Sebastien Valet, was lost to history as part of his punishment (damnatio memoriae). Almost 250 years later, the Dread Doctors managed to resurrect Sebastien's spirit and place it inside the body of their sole successful Chimera, Mason Hewitt. As with the Nogitsune during Stiles Stilinski's possession, the Beast's spirit needed time to get stronger within its new body, leading the Dread Doctors to use frequencies to trigger Mason's transformations over the course of several weeks until finally, his body shapeshifted into the exact image of Sebastien Valet, allowing Sebastien access to all of Mason's memories and skills (such as the knowledge of the names and faces of the various McCall Pack members and the ability to drive a car, technology which did not exist in Sebastien's first life in the 1700s).
- This power was utilized in all but one season: Season 2 (by Peter Hale), Season 3 (by the Nogitsune), Season 4 (by Cerberus), Season 5 (by the Beast of Gevaudan), and Season 6 (by Halwyn).