Rosia, a feline-human hybrid Myumon, balances her roles as Criticrista’s guitarist, St. MIDI Girl’s Middle School student council secretary-treasurer, and a top honor student in dance and coyness. Her self-centered charisma shines through playful gestures and sharp wit, captivating audiences and provoking rivals alike. With long pink twintails crowned by a heart-shaped ahoge, greenish-cyan eyes, and cat ears tipped with white tufts, she commands attention in her cropped sailor uniform, pink skirt, and red heels, accessorized by a heart choker, yellow headband, and thigh bells.

Initially a cunning antagonist, Rosia leverages her "once in 69 years super student" persona to dominate as Criticrista’s lead vocalist, masking her loyalty to bandmates like Tsukino, whom she comforts during crises. Her evolution reveals vulnerability as she apologizes for past manipulative tactics, prioritizing teamwork over solo ambition. A hinted backstory ties her enrollment at St. MIDI to an idol she admires, driving her relentless pursuit of recognition—a goal softened by her growing empathy. Her guitar, "White Cherry♡," embodies her musical passion, while fans cherish her affectionate "oniichan" and "oneechan" greetings, reciprocated with their "Rosia-chan" endearments.

Playful initiatives—snow sculptures, police-themed performances, meet-and-greets—and band competitions showcase her shift from rivalry-fueled antics to collaborative artistry. Relationships with Tsukino, Holmy, and Jacklyn highlight mutual support, tempering her earlier egocentricity. Standing 148 cm, she remains Criticrista’s shortest member, her pink-and-heart motif extending to alternate outfits like the fuchshaired "Black Form" and a frilly "Wedding" ensemble. Her energetic persona echoes in songs like "Happy Happy Jump!!" and heartfelt duets with Tsukino, cementing her dynamic role in both music and camaraderie.