A is one of two familiars who serve as brothers and companions to Koto. His name means "the beginning," a contrast to his brother Un, whose name means "the end," and together they are called "Ah-un" by Koto.

Bubbly and energetic, A’s hyperactive personality stands in stark contrast to Un’s reserved demeanor. The pair typically appear as chibi-style middle school students dressed in black blazers worn over red hoodies, with black pants and black shoes.

These familiars possess the ability to shift from their humanoid forms into red and blue monstrous beings capable of flight and endowed with supernatural strength. Though their exact origin remains unspecified, they were inherited by Koto from her master and father, Inari. As Inari’s creations, they are considered part of the family and are regarded as Koto's brothers.

A accompanies Koto on her journey to the Mirror Capital in search of her mother, the black rabbit Lady Koto. While in the city, both A and Un are trapped by Kurama and Yase as part of a scheme to exploit Koto’s powers. They are later freed when Koto uses her hammer, Aratama, and a sacred mirror to break out of a pocket dimension—an act that also enables Lady Koto’s return.

The familiar’s background is deeply tied to the history of the Shrine, the transdimensional organization where Koto was raised and trained. Both A and Un were present throughout Koto’s childhood at the Shrine.