Peggy Matsuyama is the eighteen-year-old female member of the Gorenger team in Himitsu Sentai Gorenger, transforming into the pink warrior Momoranger, also rendered Momorenger, and serving as the fourth member of the five-person squad. She is the daughter of a Swiss father and a Japanese mother, a background that gives her a distinctive Eurasian appearance. Before joining the team, she worked as a chemical analyst at the Hokkaido branch of EAGLE, the international defense organization formed to oppose the Black Cross Army, and she also served as a special weapons engineer specializing in explosives. When the Black Cross Army launched a coordinated assault on EAGLE's Japanese branches, the Hokkaido base was destroyed, and Peggy was the only survivor; at the time of the attack she was riding a horse during a training exercise, which spared her life. That experience of loss underlies her dedication to the team's mission of stopping the Black Cross Army and protecting innocent people.

In personality, Peggy is sophisticated, serious, and composed. She is kind toward the weak and carries herself with dignity, and she often acts as a steadying presence for her more excitable teammates, particularly the boisterous Daita and the playful Kenji, toward whom she behaves like an older sister. Off duty she is fashion-conscious, known for wearing go-go boots and short hot pants, and her stylish appearance contrasts with her deadly effectiveness in combat.

Her scientific background makes her the team's explosives and weapons specialist. As Momoranger she uses a distinctive set of tools: the Momo Mirror, a jamming device that can confuse and disorient opponents; heart-shaped Momo Cards used as throwing weapons; and high-impact Earring Bombs that she hurls with the taunt "Are You Ready? Here We Go!" She also carries a tracking and surveillance device called the Pink Cecily. Beyond her personal arsenal, she played a key role in developing the team's signature combination attacks, the Gorenger Storm and the Gorenger Hurricane. She is also a skilled master of disguise, allowing her to carry out undercover intelligence missions, and she has advanced training in equestrian arts.

Within the group, she works closely with the other rangers and frequently rides in the sidecar of the Green Machine piloted by Kenji. Her role in the story is that of the team's only female fighter, contributing scientific expertise, infiltration skills, and combat power to the unit, while her interactions with her teammates help balance the group's varied personalities. Throughout the series she proves to be a dependable, resourceful, and fearless member of the team, and her technical inventions and fighting skill are essential to the Gorengers' ongoing struggle against the Black Cross Army.