At sixteen, Nanako Misonoo expects a bright future when she enters the prestigious all-girls Seiran Academy. But her hopes are crushed as she becomes caught in a web of lies, sorrow, and resentment. Making things worse, she is selected as the newest member of the Sorority, a highly respected group within the school. Lacking the elegance, wealth, or talent of her peers, Nanako soon becomes a target of envy, especially from the intimidating Aya Misaki.
Facing growing troubles at school, Nanako writes letters to her former teacher, Takehiko Henmi, whom she calls "onii-sama." She also finds comfort in her four closest friends: childhood friend Tomoko Arikura, outgoing but unpredictable Mariko Shinobu, emotionally troubled musician Rei Asaka, and physically strong and tomboyish Kaoru Orihara.
This heartfelt drama explores the struggles of bullying, focusing on Nanako's difficult journey at her new school as she deals with vicious rumors, cruel classmates, and many social challenges.