Fumika Shinshijuin holds the position of student council president at Asakusa Girls' High School. As a member of a branch family within the influential Shijyuin clan, she harbors persistent feelings of inferiority toward main lineage figures like Kaguya Shijyuin. This drives her decision to join Rin Namiki’s fledgling Jet Racing Club, specifically to fulfill the five-member threshold for official recognition. Her core objective involves supporting Rin and Misa Aoi in defeating Kaguya during races, viewing such victories as a means to transcend her branch family status.

Fumika does not compete directly in jet races, instead providing administrative assistance and vocal encouragement from the sidelines. Interactions with Rin—such as unexpected hugs or enthusiastic attention—often trigger visible reactions like blushing or shyness, reflecting her reserved nature. Her surname, Shinshijuin, combines kanji for "fresh/new" (新), "purple/violet" (紫), "gather/assemble" (集), and "institution" (院), while her given name Fumika originates from "writing" (文).

Beyond racing, she participates in wider club initiatives like collaborative promotional video projects alongside other members, though her exact contributions remain unspecified. Her character arc centers on her initial resolve to challenge the main family’s dominance through the club’s competitive pursuits, without elaboration on subsequent personal growth or relationship dynamics.