Kagami is a tsukumogami, a type of spirit that resides within an aged object, and she takes the physical form of a small girl. Mirroring her origins, her most notable ability is tied to her true nature. Kagami possesses the power to reveal hidden truths, specifically through an ability known as the Shouyoukyou, or the Truth-Revealing Mirror. This power allows her to see into a person or object's past and discern their true essence. In practice, this appears as Kagami seeing through falsehoods to the core reality of what she observes. When she activates this ability, a circular mirror manifests on her forehead.

In terms of personality, Kagami is characterized by her lively, energetic, and emotionally open nature. She does not hide her feelings and freely expresses herself, giving her a bright and straightforward presence. This expressive personality marks a significant change over the course of her introduction. Initially, she harbored fear towards the series protagonist, Hyoma Kunato. This was a direct result of Hyoma's openly hostile and intimidating attitude toward all tsukumogami, a group he initially despised due to a past trauma.

The turning point in Kagami's relationship with Hyoma occurs during a special integration examination. Due to a misunderstanding, Kagami was attacked by a tsukumogami named Yagen. Hyoma intervened and saved her from this attack. This event drastically changed her perception of him, causing her initial fear to vanish and be replaced by an open and positive attitude. Following this incident, she becomes a friendly and important presence in his life, even taking him on what could be considered a practice date to gauge his feelings towards another character, Botan Nagatsuki. This outing also served as a training session to help Hyoma become more comfortable in social situations, particularly with girls.

Role-wise, Kagami is one of the tsukumogami living in the Nagatsuki household, a family that treats such spirits with kindness. Her relationships within this household are defined by how she addresses her companions. She uses the respectful suffix "san" when speaking to Hyoma Kunato, but affectionately calls her fellow tsukumogami, Haori and Yu, by the diminutive and familiar suffix "chan". This distinction highlights the different dynamics she shares with the human family member versus her spiritual housemates. Her own personal preference is for a specific alcoholic drink: Kahlúa milk. While her own development remains consistent, she functions as a key observer and facilitator, helping to bridge the emotional gap between Hyoma and the tsukumogami world. She is also frequently associated with another tsukumogami named Suzuri, with whom she is often paired.