Nagomi Yui, alias Cure Precious, attends Shinsen Middle School as a second-year student. Her family runs the Nagomi Diner in Oishiina Town. Her personality is straightforward and energetic, deeply influenced by her love for food and her late grandmother's motto: "food is smiles." When worried, intense hunger surges through her, compelling her to eat nonstop until the concern is resolved. She frequently misquotes idioms and phrases, and remains oblivious to romantic interest, like that shown by her childhood friend Shinada Takumi. Physically, she has purple eyes and medium-length brown hair, usually styled in twin tails fastened with magenta ribbons.

Using the Heart Cure Watch alongside her fairy partner Kome-Kome, she transforms into Cure Precious. Her signature catchphrases are "Delicious smile~!" and "I'm starving~!" In this form, her hair lengthens into bright pink, styled in thin, curled ponytails secured by turquoise scrunchies and a cone-shaped bun. Her costume consists of a light pink dress with layered skirts revealing hot pink and pale yellow ruffles, a flower-shaped apron, and a large waist ribbon. Gold spoon (left ear) and fork (right ear) earrings, a frilly headband with a bow, and boots featuring tabi-like fuchsia toes complete her look. Variant forms include the Party Up Style, sporting kimono-inspired sleeves and floral hair ribbons, and the Children's Lunch Dress, defined by a giant magenta hair bow and a checkered back bow.

Her relationships highlight her empathy. She holds deep respect for her late grandmother, Nagomi Yone, recalling her wisdom during difficult times. Open communication defines her bond with her mother, Nagomi Akiho, while she cares for Kome-Kome like a younger sibling. She connects with classmates Fuwa Kokone and Hanamichi Ran over food; they often correct her misquoted phrases. She persistently supports Kasai Amane (Gentlu), helping her overcome trauma to join the group. Despite betrayal by Godatz (disguised as Fennel), she believes in his inherent goodness and aids his redemption. Her connection to Rosemary shifts from initial friction to mutual reliance, as she disregards his overprotectiveness to defend others' happiness through food. A childhood promise to Cait Sith—to share a kids' lunch—resurfaces during the "Dreamia" theme park incident, where she comforts him and encourages atonement for his misguided actions.

The movie "Eiga Delicious Party♡Precure Yume Miru ♡ Okosama Lunch!" reveals a pivotal backstory with Cait Sith. Years earlier, she encountered him as a distraught boy and offered him a kids' lunch, vowing to make another if they reunited. When "Dreamia" manifests in Oishiina Town, she investigates its secrets with friends, recalling this promise. After Rosemary is turned into a stuffed toy by Cait Sith—now the park's director—she confronts his plan to eliminate adults, stemming from past trauma. By reaffirming their shared memory and the meal's significance, she helps him abandon destructive goals and pursue new dreams, reinforcing her belief in connecting hearts through food and compassion.

Her surname "Nagomi" blends "wa" (和), linked to Japanese culture like cuisine ("washoku"), and "mi" (実), meaning crops, reflecting her rice motif. "Yui" originates from her grandmother's wish for her to "tie" or connect people's hearts, inspired by a dish of the same name. The alias "Cure Precious" signifies something rare and valuable, symbolizing her role's importance.

Her development demonstrates growing resilience and leadership. Initially impulsive in fights—such as recklessly confronting Gentlu to prove her worth to Rosemary—she learns to balance determination with strategy. She consistently counters cynicism, whether persuading Amane that kindness deserves friendship or insisting Godatz can be saved. Resolving Cait Sith's conflict showcases her ability to merge past promises with present empathy, solidifying her theme of unity through shared joy in food.