Nene Onemine attends Itan Private High School, starting as a first-year classmate of Shoko Komi and Hitohito Tadano and progressing to the third-year class. Her name reflects her personality: "Onemine" suggests "onee-san" (older sister), and "Nene" resembles "nee-chan" (affectionate term for older sister) or the attention-getting "Ne! Ne!" in Japanese. She embodies an observant, caring, "big sister" archetype. Physically, she has brown hair and eyes, stands 165 cm tall, and possesses a mole under her left eye and another near her lower lip. She has four younger siblings: twin brothers Kazuya and Takeru, and sisters Nono and Nana. Kazuya and Nono call her "nee-chan," highlighting her nurturing role. During a Valentine's Day baking session at home, she supervised her siblings and friends Komi and Kaede Otori, demonstrating patience and responsibility. She gently redirected the children's questions about Komi's shyness. Her siblings' names carry puns: Kazuya's bluntness evokes "arrows for target practice," Nana sounds like "seven" (her approximate age), and Nono suggests a child's term for "divine figure." Academically, Onemine moves from first-year Class 1 to third-year Class 3. Her first formal interaction with Tadano involved assisting him with student council paperwork; her perceptiveness allowed her to deduce Komi's jealousy and the mutual romantic feelings between Komi and Tadano, prompting her to leave them alone. She frequently supports Komi during school events: joining Komi and Otori for culture festival preparations, comforting Komi when she struggled to interact with cats at a cat café, and later sharing a photo of Komi with a cat to Tadano. After the festival, she signed Komi's "friend book" as the 13th friend. Onemine shares a particularly close friendship with Kaede Otori, often seen holding Otori's hand to prevent her wandering. They collaborate on activities like making rice balls for the festival, visiting the cat café, and participating in a Christmas party where Onemine massaged Tadano's shoulders during a "King Game." On school trips, like the one to Kyoto, she encouraged peers such as Agari Himiko to join group baths and later appreciated handmade gifts from Inaka Nokoko. Her development remains consistent, retaining her supportive, observant nature throughout high school. She mediates social situations and fosters inclusivity without seeking attention. Managing her younger siblings at home explains her patience and adeptness in group dynamics at school.