Sumi Yabuuchi serves as Madoka Yabuchi's older sister. She holds a nursing position at Kanagawa National Hospital, where her specific responsibility involves acting as the primary nurse for the hospitalized patient Yuka Kurumatani. This medical role directly links her to the Kurumatani family through Yuka's condition. Her presence at the hospital also creates a situational connection to other characters involved with Yuka's situation. Her established character role, centered on her family connection and occupation, remains consistent throughout the documented narrative without significant evolution or additional background details.