Hikari Momoyama is Mirai Momoyama's younger sister. Her family operates the bakery Pâtissière La Peche, managed by her mother, while her father occasionally earns the nickname Mr. Whip.

Physically, Hikari shares indigo eyes and peach-colored hair with her mother and sister. She styles her hair in short curled pigtails secured by pale orange bows, featuring straight-cut bangs centered on her forehead and thin strands framing her ears. In later seasons, her pigtails grow longer, her ribbon accessories upgrade, and her forelock strands develop a slight curl.

Personality-wise, Hikari displays maturity beyond her years but frequently exhibits bluntness, particularly toward her older sister Mirai, whom she tends to tease or doubt. Beneath this critical exterior, she harbors underlying care for her family, though she struggles to openly convey supportive feelings. She is easily annoyed and forthright with her opinions, even toward her parents. Childlike traits emerge through her enjoyment of drawing, regular napping, susceptibility to fatigue, and assistance at the family bakery; she notably critiques her mother's lack of business acumen.

Her relationships include classmates Devi Fudo and Luu Asuka, who nickname her "Little Yama" (妹山), referencing her status as the youngest Momoyama sibling. This trio develops closer bonds in later episodes when Hikari dedicates significant effort to coaching them through practice sessions for their debut performance.

An initial plan for her to join the Oshama Tricks unit was reportedly scrapped due to production constraints. Her name carries symbolic meaning: "Momoyama" (桃山) combines "peach" (桃) and "mountain" (山), while "Hikari" (ひかり) translates to "light".