Koma is a bakeneko, a demon cat spirit originally assigned to protect Tadahiro Amatsu's grandfather. This duty creates her enduring bond with Tadahiro's family line. She shapeshifts between three distinct forms: a standard black cat, a cat-woman hybrid, and a fully human guise appearing as a woman in her mid-to-late twenties. Her human and hybrid forms allow her to engage directly in combat when needed.

Her primary purpose is guarding Tadahiro Amatsu, cousin to the Hieda sisters, due to his spiritual importance and the supernatural dangers he faces. She lives and operates within the Asagiri Shrine alongside the Hieda family. While not a frontline fighter like the Miko Council, she steps in to defend Tadahiro or the shrine against direct threats.

Koma presents a stern, sharp-tongued, and often short-tempered demeanor, especially when her duties are questioned or she encounters disruptions. Despite this serious nature, she possesses a notorious weakness and excessive fondness for cake, revealing a contrasting facet of her personality. Her steadfast loyalty remains solely focused on Tadahiro and his family, continuing her protective role across generations.