Uiui is a female Myumon of the Ice Rabbit race from a distant ice-covered Northern European homeland. Her early life centered on daily ice skating in an entertainment-scarce environment, forging a deep longing for music after witnessing a band's televised live performance. This pivotal moment drove her relocation to MIDICITY to pursue musical ambitions.

She possesses light blue bobbed hair, golden yellow eyes, translucent white skin, and a light blue fluffy cotton round tail. Her attire features a black top with a sky blue ribbon, black shorts with sky blue details, navy shoulder bracelets, a dark blue scarf with a sky blue line, black gloves with sky blue bows, a snowflake hair clip, a hip-strapped blue bag, and dark blue boots. A consistently blank expression reinforces her ice-cold demeanor.

As vocalist and bassist of REIJINGSIGNAL, she wields the bass "Snow Wizard." Her personality is cool-headed and knowledge-driven, frequently affirming with the French "oui" and ending sentences with "zeyo." Her motto—"I will seize everything I want with my own hands"—reflects determined pragmatism. She prefers cold climates and foods, openly disliking heat, hot meals, and sticky situations.

Background includes part-time work as a cold storage warehouse manager and bookstore employee, aligning with her temperature preferences. Frequent childhood relocations caused occasional linguistic idiosyncrasies. In REIJINGSIGNAL, she collaborates with bandmates Rararin and Sumomone, notably contributing ice cream to their "perfect sukiyaki formation."

Uiui expresses nostalgia for her homeland's simplicity, recalling singing and skating with joy. She remains confident in her ice skating skills and occasionally references harnessing a "blizzard's force" during performances. Character episodes like "Ice Sculpture Divination, Zeyo" and "The Ring's Meaning Is a Secret, Zeyo" imply nuanced personal experiences. Interactions begin reserved, requiring acknowledgment before familiarity is granted.