She the main character of the Japanese light novel and anime series Maria-sama ga Miteru created by Oyuki Konno. In the beginning of the series, Yumi is bashful beyond words, very timid and unsure of herself. She first met Sachiko, the star of Lillian School and had her tie fixed by Sachiko, which mortified Yumi. Yumi's friend, Tsutako Takeshima, took a cute picture of this and wanted to display it in the school festival. Tsutako got Yumi to ask permission from Sachiko. Other characters often comment on how her emotions 'show on her face'.
In the second season, Yumi is Rosa Chinensis en bouton. She has no petite soeur yet, but fans think it might be either Matsudaira Touko or Hosokawa Kanako.