To elder brother

Nanako Misonoo is a young high school freshman at the exclusive girl's school Seiran School. When she begins her first year at this school, she falls into a world of female rivalry, love, chaos, and heartbreak. She narrates the story of the series in a series of letters to a young man named Takehiko Henmi, who she calls "Oniisama" (Brother). In reality, Takehiko was her teacher at the cram school she went to earlier. She feels such a strong bond with him that she asks if she could continue corresponding with him. He agrees, and soon she begins writing to him as a "brother." When Nanako starts her new school year at the all-girl Seiran School, she is unexpectedly inducted into the school's Sorority despite having none of the looks, talents, or background needed to become a member. As the series progresses, she becomes involved in the lives of the "Magnificent Three", the three most popular girls in the school.
As Nanako continues to interact with these women, she becomes attached to the great but troubled Rei Asaka, whom she wants to help, but cannot get close to due her obsession with Fukiko Ichinomiya, the Sorority president. Nanako also becomes friends with a beautiful and lonely young girl named Mariko, who is determined to get into the Sorority and make Nanako her best friend at all costs. Meanwhile, Nanako has problems of her own; she is constantly being bullied by her peers due to her membership in the Sorority despite not having any of the requirements. Throughout these problems Nanako is supported by her childhood friend Tomoko, the athletic but secretly ailing Kaoru Orihara, and the correspondence with her "brother", who just happens to have some secrets of his own. The series chronicles her first-year at Seiran Academy as she uncovers the past of some of the most popular girls in school, learning of love, loss, and her own family's secrets, including her true relation with Takehiko.

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