Fumika Shinshijuin holds the position of student council president at Asakusa Girls High School. She joins Rin Namiki's Jet Racing Club solely to meet the five-member requirement for its official recognition, enabling the club's formation. This action is driven by her desire for Rin and Misa to defeat Kaguya Shinshijuin; Fumika feels deep shame over being treated as inferior due to her status in a branch family of Kaguya's main lineage. She does not race herself, instead providing support by cheering on Rin and Misa and offering encouragement during their competitions.

Her interactions show a degree of shyness in close personal situations, particularly when faced with Rin's enthusiastic behavior. Instances where Rin employs a pleading style or hugs her in the student council room cause Fumika to blush noticeably. Her surname, Shinshijuin, combines the characters for "fresh, new" (新), "purple, violet" (紫), "assembly, collection" (集), and "hospital" (院). Her given name, Fumika, incorporates the character for "writing" (文).