Kuzuha Togashi is the younger sister of Yuuta Togashi and the second child in the Togashi family, which includes her parents, younger sister Yumeha, and older brother Yuuta. She ages from 13 in the first season to 14 in the second season and 15 during the movie timeline, standing 143 cm tall. Kuzuha exhibits a responsible and practical nature, frequently assisting with household chores. Shinka Nibutani observes her laidback demeanor resembles Yuuta's. Having witnessed Yuuta's middle school "chūnibyō" phase where he adopted the "Dark Flame Master" persona, Kuzuha finds his past behavior intensely embarrassing and actively distances herself from it socially. This is clear when she tries to prevent her friend Mika from noticing Yuuta's chūnibyō antics during a nighttime stationery shop errand, fearing social humiliation. Despite this, she cares for her brother, later reflecting on Mika's comment that Yuuta seemed "cool," though she ultimately prefers his ordinary self.

Her role grows in the second season when she temporarily moves in with Yuuta and his girlfriend, Rikka Takanashi, to help manage the household after their parents and Yumeha relocate to Jakarta for their father's work. During this time, she supports Yuuta's relationship with Rikka and occasionally teases the couple, causing them both embarrassment. Following the events of the movie *Takanashi Rikka Kai*, Kuzuha moves to Jakarta with her mother and Yumeha to join their father. She later returns to Japan to continue her education, rejoining Yuuta during the second season. Kuzuha has neck-length black hair and green eyes. Her name, translating to "Camphor tree leaf," connects to nature, complementing her surname Togashi, meaning "wealth, abundance" and "evergreen oak."