Musubi Tendōji, a 16-year-old student council president at St. Corsica Academy, commands respect as the institution’s "perfect girl"—a title earned through academic brilliance, athletic prowess, and unshakable poise. Yet beneath this flawless exterior lies a timid soul burdened by self-doubt and a deeply ingrained fear of imperfection. Forced into molding herself to societal ideals since childhood, she hides vulnerabilities like her insecurity over her singing voice and a cautious aversion to risk.

Her life shifts when meeting Haru and Rona at NANASUTA, an encounter that nudges her toward the uncharted world of idolhood. Initially rejecting the idea, fearing her authentic voice clashes with her cultivated image, she hesitantly joins 777☆SISTERS and subunit NI+CORA upon realizing their appreciation for her true self. This leap sparks her transformation, as she begins embracing her quiet love for singing and unassuming nature, shedding the weight of external expectations.

Sporting long dark-blue hair with cropped bangs, Musubi’s disciplined demeanor is mirrored in her crisp school uniform. Her surname, Tendōji, weaves symbols of "heavens," "public chamber," and "Buddhist temple," while "Musubi" playfully echoes the Japanese term for "rice ball." As an idol, she adopts whimsical costumes like a yakisoba-themed outfit, contrasting her formal attire, and mines self-deprecating humor from her vocal struggles. Through these experiences and bonds with her group, she gradually merges her fractured identities, discovering freedom in authenticity and the courage to redefine perfection on her own terms.