Tsumugi is a human girl first encountered as a living doll following a puppet show. She has long wavy dark blue hair and navy eyes. In the fabricated Doll Kingdom, she wears a distinctive red and white dancing dress with white sleeves, an apricot pink ribbon at the waist, and a red rose on the chest, along with long gloves, socks, and red shoes adorned with white ribbons. A pink hat featuring a large red rose completes her attire.

Her defining characteristic is a profound passion for ballet. This passion is shattered when the Phantom Empire commander Black Fang afflicts her with invisible anklets, robbing her of the ability to use her legs. Confined to a wheelchair in the real world and plunged into deep despair, she withdraws from friends and family, abandoning her once-signature smiles. Exploiting this vulnerability, Black Fang lures her into the Doll Kingdom, promising a place where she can dance freely. He manipulates her by claiming the Pretty Cure threaten this paradise and grants her the ability to control Saiarks to attack them. Unbeknownst to Tsumugi, Black Fang engineered her disability specifically to harvest her despair as a power source.

Within the Doll Kingdom, all residents are sentient versions of Tsumugi's own dolls. Prince Zeke, her most cherished doll, spearheads their devotion to maintaining her happiness despite the kingdom's artificial nature. Embracing the illusion, Tsumugi orchestrates Saiark attacks against the Pretty Cure under Black Fang's influence, isolating the protagonists by transforming allies like Seiji Sagara, Blue, and the mascots into dolls.

Her pivotal moment arrives when Cure Lovely confronts her within a cage of despair threads crafted by Black Fang. Lovely's insistence on helping her—coupled with Prince Zeke and the dolls sacrificing themselves to breach the cage—triggers Tsumugi's realization that genuine happiness requires confronting reality, not escaping it. She rejects Black Fang's lies and collaborates with Lovely, converting her despair into hope. This transformation enables Miracle Lights sent by supporters worldwide to empower Lovely's victory.

Following Black Fang's defeat, Tsumugi returns to the real world, regaining her ability to walk and dance. Her resolve crystallizes: she will pursue ballet professionally, aiming to inspire others through her performances. Her recovery culminates in a ballet recital attended by the main characters, symbolizing her reintegration into life and her dreams.

Tsumugi's only other canonical appearance is a non-speaking cameo walking on a street in episode 49 of the series.