Shinjyu Harumi, the ten-year-old third daughter of the Harumi family running the Uoharu fish market shop, assists in the family business alongside her older sisters: nineteen-year-old Sawara and fourteen-year-old Kajika. Though young, Shinjyu displays a maturity and realism in her speech and demeanor, contrasting with an underlying desire to behave more childishly—a desire held back by her strong self-awareness and practical nature.

Her full name carries maritime connections: "Shinjyu" potentially derives from the word for pearl, while "Harumi" combines "Haru" (晴, clear/sunny) and "Mi" (海, sea). She stands 134 cm tall, weighs 32 kg, and has blood type A. Born on August 28th under the Virgo sign, her interests include accounting and collecting frog-themed charms.

Shinjyu performs as part of the idol group 777☆SISTERS, active in subunits Sanbon Ribbon and the indie group KODOMO RENGO. Her recruitment completed the idol project Nanastar as its twelfth and final member.

By 2043, Shinjyu is a university student studying economics. Her appearance has evolved, featuring increased height and a hairstyle recalling her 2036 look. Her core personality persists: pragmatic, perceptive of others' emotions, and quick-witted. Within her new unit, SEASON OF LOVE, she embodies the "Spring" motif and assumes an older sister-like troubleshooting role. Her hobby of collecting frog-themed items endures.