Void kitsune in their spirit guise possessing a host, sport, plaque white eyes with chrome fangs, amongst other demonic features afterwards.
Kitsune, in their younger years, naturally possess an aura in the shape of a flaming fox.
Initially this aura is only visible to beings with a supernatural vision, or by use of a developed image using flash photography. They can eventually learn to mask, conceal this aura to hide themselves. In Illuminated, Kira shows Scott her then unidentified aura via a photo. Later on, he locates Kira using his werewolf vision and sees her Fox-shaped aura around her frame in full detail.
In the heat of battle, Kira's aura would become naturally visible. It would flare up all around her, she'd experience losses of control and an innate bloodlust, even coming close to killing her mother. Noshiko explains this is due to the power within Kira being in conflict and out of balance between Kira's human side and the Fox.
In A Novel Approach, Scott witnesses Kira's Evolved aura with his werewolf vision when he and Kira are looking for Kira's belt sword. The Fox Spirit has grown from simply encasing and shielding Kira to flaming all around her, grown in size and had taken on a more threatening shape. It has also become separate from Kira as the Fox points out the location of the misplaced sword to the werewolf with Kira none the wiser.