Yuna Kamihara (full name written as 上原ユウナ in kanji) begins as a 10-year-old Okinawan elementary school student residing on fictional Izayoi Island in the Ryukyu Islands. Her mother perished during a typhoon when she was an infant, and her marine biologist father’s frequent absences mean she primarily lives with her supportive, wisdom-sharing grandmother. Her late grandfather taught her karate before departing, gifting her special moonsand as a training good-luck charm. She earns a black belt and becomes sensei of her island’s dojo. Her routine life shifts dramatically upon meeting Stitch, an extraterrestrial who crash-lands on Izayoi, sparking their profound friendship. Through Stitch, she bonds with characters like Jumba, Pleakley, various experiments, and supernatural beings such as the yokai Kijimunaa.

Yuna’s personality merges kindness and politeness with fierce protectiveness against injustice, bullying, or crime. She displays confidence and leadership, often taking impulsive charge during crises. Her karate skills focus on defense and aiding others, not aggression. A playful, competitive streak surfaces in friendships, including lighthearted rivalries with Stitch. She masks emotional vulnerability, internalizing stress until breaking points trigger anger or tears under pressure. Thunderstorms remain her sole acknowledged fear, countered by superstitiously rubbing her belly button for luck afterward. Academically, she struggles, particularly in mathematics, frequently scoring low on tests. Her design features brown hair in spiky ponytails—initially with blue beads, later with green scrunchies—and a signature red sleeveless dress patterned with yellow flowers. Early seasons show her in striped sweatpants and pink sandals, transitioning to denim and orange sneakers later. Specific outfits include a pink nightgown for sleep, a red swimsuit, and a white karategi during training.

Character arcs unfold across seasons. In season two (Stitch! ~The Mischievous Alien's Great Adventure~), her cousin Tigerlily moves in, initially bullying and manipulating Yuna—such as coercing chores via blackmail—though later rationalizing this as misguided mentorship. Season three (Stitch! ~Best Friends Forever~) relocates 11-year-old Yuna with Stitch, Jumba, Pleakley, and Tigerlily to urban New Town on Okinawa’s main island, where she adapts to city life and a new school. Tigerlily’s demeanor softens significantly here. The episode "Stitch's Dreams" depicts Yuna turning 12, marking her shift into early adolescence. Her Okinawan heritage informs cultural elements: her name derives from the local term for sea hibiscus ("Yuna"), and her surname Kamihara (meaning "upper plain") reflects the Ryukyu Islands' pronunciation of the kanji 上原, revealed formally in season three’s premiere. Throughout, her strong moral compass drives alliances with Stitch against antagonists like Dr. Hämsterviel and rivals such as Penny.