Yumi leads the elite shinobi team at Gessen Girls' Academy. Orphaned young when her parents died on an unknown mission, she was raised by her grandfather, Kurokage, a rival to the legendary Hanzō. Kurokage trained her alongside fellow orphans Murakumo, Shiki, Yozakura, and Minori in a remote mountain area, subjecting them to rigorous, life-threatening drills. Initially fueled by revenge for her parents, Kurokage steered her towards using power for a greater purpose: his dream of a world free from evil. This ideal, the "Justice of the Moon," became her core philosophy, defining true happiness through the eradication of evil.

She possesses medium-length gray hair, pale skin, and light blue eyes, typically wearing a white ribbon. Her standard shinobi attire is a white furisode kimono with blue trim, featuring exposed shoulders and cleavage, paired with white socks or lavender flip-flops. During her "Ice Queen" combat transformation, her hair lengthens and turns icy blue, her eyes shift to red, and she loses her hair tie, adopting a more formidable presence.

Yumi is characterized by calmness, seriousness, and stubborn adherence to her ideals. Initially inflexible, she dismissed opponents like Asuka for lacking sufficient skill. Her leadership blends firmness with underlying care for her teammates, though she often pushed them excessively in training, forgetting the need for rest. Over time, she grew more lenient, delegating discipline to Yozakura while remaining deeply committed to her comrades' well-being. Confronting her own hypocrisy and black-and-white morality after battles with Asuka and Homura led her to acknowledge moral nuance and extend friendship to former rivals.

In combat, Yumi wields ice-based techniques rooted in Kurokage's teachings. Her signature abilities include "Black Ice," conjuring frigid lances to pierce opponents, and "Ice Pillar Fan," creating whirlwinds of icicles. In the OVA *Festival Eve Full of Swimsuits*, she demonstrated tactical awareness by organizing a water-based cavalry battle to resolve conflicts during a spa resort truce. When supernatural enemies blocked standard transformations, she activated "Super Frantic Mode" alongside others, sacrificing clothing for heightened speed and power to overcome the threat, exceeding her initial premonition of a significant battle.

Her development highlights a shift from rigid idealism to pragmatic openness, influenced by interactions with other shinobi schools, leading her to recognize the interdependence of good and evil. Her background losses and Kurokage's mentorship continued to shape her actions, evident in her intense reaction to Hanzō's disrespect towards her grandfather's memory, which ignited her conflict with Hanzō Academy.