Erika Kurumi transforms into Cure Marine, a Pretty Cure member residing in Kibougahana City with her family. Her mother runs the Fairy Drop fashion boutique, while her father works as a cameraman. An older sister, Momoka, is a fashion model whose success initially fuels Erika's jealousy and insecurity about her own appearance and talents. As a second-year junior high student at Myōdō Academy, she struggles academically, often seeking help from classmates. Her passion lies firmly in fashion design and trends, driving her to found and lead the school's Fashion Club, recruiting members including Tsubomi Hanasaki and Itsuki Myoudouin.

Erika presents an energetic, blunt, and outwardly confident personality, frequently speaking her unfiltered thoughts, sometimes causing unintentional hurt. Yet beneath this lies a strong sense of justice and loyalty, especially towards loved ones. Her initial motivation for becoming a Pretty Cure centers on protecting her sister, later expanding to safeguard her friends and the city. Her character development shows growing interpersonal awareness and empathy, particularly through her partnership with Tsubomi, learning to temper impulsiveness with consideration while retaining her spirited core.

As Cure Marine, hailed as "the flower fluttering in the ocean winds," she wields powers tied to water and the ocean. Her transformation and attacks—Marine Shoot, Marine Dynamite, and the collaborative Double Body Punch with Cure Blossom—feature aquatic motifs. Her theme color is blue, symbolizing the blue daisy, with her Cure form displaying light blue hair contrasting her civilian dark blue. A defining moment sees her create her catchphrase, "Even with a heart wider than the ocean, this is my limit!", during a crucial battle rescuing Momoka from becoming a Desertrian, showcasing her resolve. She confronts the Desert Apostles fearlessly, sometimes independently facing high-ranking foes like Kumojacky. Her combat style emphasizes agility and direct confrontation, complementing Cure Blossom's strategy. Teamwork is central; her synergy with Cure Blossom evolves from friction into a deeply coordinated partnership enabling powerful combination attacks. The narrative contrasts her bold Cure persona with her civilian acrophobia.

Key relationships shape her journey. Her bond with Tsubomi starts when recruiting the shy transfer student into the Fashion Club instead of Gardening Club, creating a dynamic where Erika's extroversion balances Tsubomi's reserve. Their friendship deepens through shared Pretty Cure duties, with Erika offering encouragement during Tsubomi's self-doubt. With Yuri Tsukikage (Cure Moonlight), Erika moves from perceiving her as cold to respecting her experience and resilience. Her relationship with Momoka evolves from envy and rivalry to mutual admiration and support after Erika confronts her insecurities. She also leads and supports friendships within the Fashion Club, helping members like Nanami Shiku balance obligations and self-fulfillment.

Her background highlights a transformative arc. Joining Pretty Cure for immediate personal stakes—protecting Momoka—she embraces broader responsibility for the community and the Heart Tree. Key developments include overcoming her jealousy of Momoka, catalyzing her first transformation and authentic catchphrase. She matures from an abrasive individual into a more reflective, supportive teammate valuing collaboration over solo heroics. This growth is tested in battles like her intense confrontation with Kumojacky, showcasing increased determination and refined skills. Supplementary media notes her continued aspirations.