Hikari Momoyama, the younger sister of Mirai Momoyama, lives with her parents and older sister. Her mother runs the bakery Pâtissière La Peche, where Hikari sometimes helps, though Hikari feels her mother lacks business sense. Her father is known as Mr. Momoyama or Mr. Whip.

Physically, Hikari possesses indigo eyes and peach-colored hair. Initially, her hair features short curled pigtails held by pale orange bows, straight-cut bangs bunched at her forehead, and thin strands near each ear. By the second season, her pigtails grow longer and gain ribbon adornments, while her forelock strands develop a slight curl.

Her personality blends maturity with childlike qualities. Often blunt and easily annoyed, particularly towards Mirai whom she frequently teases or doubts, Hikari nonetheless harbors underlying care and support for her family, even if she struggles to express it openly. Pragmatic even with her parents, she engages in typical childhood activities like drawing, playing, and napping, tiring easily.

Hikari's primary relationships are with classmates Devi Fudo and Luu Asuka, together forming the group Oshama Tricks. They nickname her "Little Yama," referencing her status as the youngest Momoyama sister. While sometimes appearing reluctant, she demonstrates loyalty to them, such as dedicating significant effort to coach them for a performance to help an ill Bugcchu, an experience that strengthened their friendship.

Her development shows a gradual reveal of her supportive nature. Though typically critical of Mirai's endeavors, like dismissing her idol potential by predicting low followers, she participates in family mediation during conflicts. Her involvement with the Oshama Tricks further highlights her capacity for mentorship and teamwork.

A scrapped concept involved her performing with the Oshama Tricks, prevented by production issues.