Fumika Shinshijuin

She is the student council president at Asakusa Girls High School and joins Rin Namiki's Jet Racing Club so that the club can have a fifth member and be officially recognized as a club. She does this as she wants Rin and Misa to defeat Kaguya Shishuuin, as she is ashamed of being treated as lesser due to being from a branch family of Kaguya's.

Fumika does not participate in the races, and mostly just cheers Rin and Misa on, encouraging them to defeat Kaguya.

(Source: Kandagawa Jet Girls Wiki)