|“|| Scott: "Allison, please tell me that you have something. They're here. [...]"|
Allison: "Okay, okay, listen-- they're Japanese demons. They're called the Oni. They're looking for someone possessed. Someone with a dark spirit attached to them."
Scott: "A Nogitsune. [...] Just tell me what else."
Allison: "Okay, they won't hurt you. They know you're supernatural, but once they do this check, once they realize that you're not carrying with you this dark spirit, they won't hurt you, I promise."
In Teen Wolf, Supernatural Scanning is the power to sense something that is otherwise not perceivable by normal human senses. It is a natural power used by the Oni to search for individuals who have been possessed by spiritual creatures, as their ability allows them to detect who is truly themselves and who is not. It can also be an artificial power, as the Dread Doctors bestowed upon themselves the means to sense the location of any supernatural or unnatural creature by honing in on their unique frequencies using a pair of old-fashioned goggles.
Natural Users of Supernatural Scanning
The Oni are the only known natural user of this power, which they utilize in their pursuit of beings who are possessed by dark spirits. They were first seen using this power in Season 3B, after the ancient Celestial Kitsune Noshiko Yukimura used a summoning ritual to conjure the Oni in Beacon Hills to assist her in hunting the Nogitsune, which had been released from its cage in the roots of the Nemeton. The Oni uses this power by making prolonged eye contact with their target, as their glowing yellow-green eyes (caused by the glow of the fireflies that animate them) scan their targets to determine whether they are truly themselves or are possessed. This power is used in conjunction with their power of branding in which those beings they deemed to be free of possession had the jiko, or onore, kanji burned into the skin behind their left ears with their right index fingers.
This power was used on Isaac Lahey, Ethan Steiner, Derek Hale, Lydia Martin, Aiden Steiner, Scott McCall, Kira Yukimura, and Stiles Stilinski. In Stiles' case, the Oni were unsuccessful in their first attempt to perform their scan on him due to his possession by the Nogitsune, who had gained a considerable amount of strength from the chaos, strife, and pain he had caused and subsequently fed upon to the point of being able to kill three of the five Oni Noshiko had summoned; the second time, the scan was successfully performed by the Oni, who determined he was more himself than he was the Nogitsune following the Void Kitsune's evacuation from Stiles' body.
Unnatural users of Supernatural Scanning
The Dread Doctors, human doctors who used science to give themselves powers of electromagnetic manipulation, memory manipulation, and extended lifespans, were able to locate their Chimera creations and other supernatural creatures by honing in on their specific, unique frequencies. This is either a power derived from their masks or a gained power that was amplified and focused by the masks. The Dread Doctors also crafted a pair of goggles, which the Werecoyote Malia Tate used to track her biological mother and fellow Werecoyote Corinne, despite having virtually no memories of her and having not truly met her since she was a newborn.
This power was first seen in use by the Dread Doctors in both parts of Season 5, as they used it to track down the Chimeras they created in order to locate and continue their experiments on these unwilling test subjects by performing medical procedures and even killing them if they rejected their transformations and were thus deemed failures. This power was used on Tracy Stewart, Donovan Donati, Lucas, Josh Diaz, Hayden Romero, Corey Bryant, Beth, and Noah Patrick.