Erika Kurumi transforms into Cure Marine, a water-themed magical warrior with a floral motif symbolizing "the flower swaying in the sea breeze." She resides above her family's Fairy Drop fashion boutique in Kibougahana with her parents and older sister Momoka. Initially jealous of Momoka's modeling success due to shared childhood aspirations, Erika later shifted her focus to fashion design. As Cure Marine, she wields the Heart Perfume for transformations and executes attacks like Marine Shoot. Her upgraded forms include Super Cure Marine, characterized by elongated hair, lighter blue hues, expanded gloves, and heightened attack capabilities, and Rainbow Cure Marine, featuring feather-like embellishments and wing motifs. Her catchphrase proclaims: "Even if my heart is larger than the sea, I have reached my limit!" Erika exhibits high energy, bluntness, and curiosity, frequently acting before thinking. She employs color therapy to interpret emotions through clothing. Despite occasional immaturity or laziness, she demonstrates fierce loyalty—particularly toward best friend Tsubomi Hanasaki (Cure Blossom)—whom she supports through insecurities. Her dynamic with fairy partner Coffret alternates between camaraderie and conflict, resembling sibling interactions. In *New Stage: Mirai no Tomodachi*, Cure Marine battles the entity Fusion in Yokohama alongside Cure Blossom and other Pretty Cures. She coordinates attacks against Fusion's spawn and aids the Smile Pretty Cure! team against the reborn Fusion. She reappears in *New Stage 3: Eien no Tomodachi*, delivering speaking lines during dream-world confrontations against nightmares. Her character development resolves jealousy toward Momoka through recognizing their separate paths. During the "Shadow Cure" trials, she readily accepts her flaws due to inherent self-assurance. Her journey emphasizes finding purpose as a Pretty Cure, where protective abilities solidify her sense of belonging.