Kagami is a tsukumogami, a spirit inhabiting an aged object and gaining physical form. She lives among five others in the Nagatsuki house, forming a benevolent family unit dedicated to serving and protecting Botan Nagatsuki. Her name, meaning "mirror" or "looking glass" in Japanese, directly signifies her origin as a mirrored object.

She exhibits a timid and conflict-averse personality, displaying nervousness during confrontations. This was evident when she apologized for lateness upon meeting Hyoma Kunato and became frightened by escalating tensions between Hyoma and the other tsukumogami. Kagami attempted to intervene and stop the fighting, but Nagi yelled at her, causing her to apologize again out of fear. Her demeanor contrasts with the more aggressive tsukumogami in the household.

Her abilities stem from her mirror nature and involve defensive reflection-based powers. No details regarding her creation, early existence, or documented evolution across the series—including significant changes in her role, relationships, or abilities—are available.