Originating as a black rabbit formed by Koto from charcoal before she entered the Mirror Capital, Un serves as Koto's first companion and cherished friend, embodying Koto's innate creative power. Un shifts into a humanoid form resembling a young girl with dark hair and prominent rabbit ears. In this state, she exhibits fierce protectiveness and unwavering devotion towards Koto, driven by a singular focus on ensuring Koto's happiness and well-being, often displaying stubborn determination.

Un accompanies Koto into the Mirror Capital. When Koto becomes separated from her family and loses her memories, Un remains steadfastly by her side, holding onto the memory of their bond and Koto's true nature. She persistently attempts to remind Koto of her origins and powers, though Koto initially dismisses these efforts.

A significant conflict erupts when Koto expresses a desire to escape the Mirror Capital. Un vehemently opposes this, believing departure would endanger Koto and sever their connection to the city and its inhabitants, especially Myoue. Un's protective instincts manifest as intense possessiveness, culminating in a physical confrontation where she attacks Koto to prevent her leaving.

During this struggle, Koto defends herself using her mallet, striking and shattering Un, seemingly destroying her. Yet, Un's essence persists within the Mirror Capital. Later, confronting the entity threatening the city's stability, Koto uses her power not for destruction but for creation. As part of this act, she recreates Un.

Following this recreation, Un exists in a fully human form, now without rabbit ears. She retains all memories of her past existence as the black rabbit and her profound bond with Koto. This new human form represents a continuation of their relationship on a different level. Un lives peacefully within the stabilized Mirror Capital alongside Koto and the others.