Yanagin's Senior is a third-year student at Sanada Central High School. She frequently mentors the "High School Girls are Funky" trio—Yanagin, Ikushima, and Habara—during their gatherings at Habara's residence, focusing her efforts on boosting their "high school girl power," though these attempts usually fail. She shares a long history with Ikushima's Senior and Habara's Senior, beginning in elementary school. A pivotal incident occurred in third grade when misplaced lunch money led to accusations against Yanagin's Senior and Habara's Senior. Both denied responsibility and blamed each other, leaving the true culprit unknown. This unresolved conflict fueled a decade-long feud between them. The matter was finally settled when Ikushima's Senior admitted misplacing the money, allowing Yanagin's Senior to let go of her grudge. Physically, she is relatively tall with broad shoulders. She has black eyes and waist-length, untied black hair with face-framing bangs. She typically wears her Sanada Central High uniform without the coat and ribbon. Her personality is loud, energetic, and quick-tempered. She readily engages in crude arguments and physical fights. She holds unique, often exaggerated, beliefs about the popularity and appeal of high school girls, which frequently shape her advice to the trio. Despite her abrasive nature, she demonstrates forgiveness, as seen when she moved past the elementary school incident after learning the truth. She also expresses remorse for past actions that harmed others, particularly concerning Karasawa.