Tomoko has been Nanako's best friend and support since childhood. Because of Nanako's admission in the Sorority their relationship - and the trust Tomoko has in Nanako - will be affected negatively.

Differently from the manga, however, in the anime this rift, caused by some lies told by Mariko, will be resolved, and Tomoko will always be by Nanako's side, inciting and helping her as usual in her moments of despair or difficulty.

With the passing of time, Tomoko will also become friends with Mariko, and will defend her in front of the others more than once.

Tomoko's presence in the anime helps in giving a tone of "normality", and helps the viewer not to lose the contact with real life: while all the girls at Seiran base their lives on the Sorority's activities, making of them a matter of life and death , Tomoko always shines in her simplicity, letting the viewer breathe in relief...

Before leaving her cram school, Nanako Misonō asks one of the teachers if they can become pen-pals. The teacher, Takehiko Henmi, is reluctant at first, but eventually accepts the offer. The story is narrated through the letters sent from Nanako as she enters Seiran, a renowned private high school for girls only. There she encounters many difficulties as an ordinary middle-class girl invited to the prestigious Sorority, the most traditional and sophisticated club on campus.. 
(Source: AnimeNewsNetwork)

A classic manga about girls at a private all-girls school. The storyline centers around the experiences of Nanako, a "normal" girl who is invited to join the prestigious school organization, the Sorority, and is resented by all the other students because she doesn't appear to be qualified. Other key characters are Nanako's two friends: Tomoko, her friend since childhood who is alienated by Nanako's decision to try to join the Sorority, and Mariko, a strange, obsessive girl who is invited to join the Sorority along with Nanako; her "older brother," Henmi, who she corresponds with by mail; and the "Three Magnificent Ones," all of whom are admired and quasi-worshipped by the rest of the student body: the head of the Sorority, Miya-sama, the haunted, pill-popping rebel, Saint Juste, and the star athlete with a mysterious disease who doesn't like the Sorority, Kaoru-no-kimi. (Source: Lillicious) 
 
Included one-shots: 
Volume 2: Summer in Canterbury 
Volume 3: Early Spring Trembling

Tomoko Arikura