In the beginning, the name of this character often appearing in Takehiko's company is never mentioned. He's Henmi's good-humoured and genial friend and university colleague. The first time we see him alone is in the building where Saint Just lives, and in time we'll discover how he's related to Rei...   He likes Mariko Shinobu, and will try very patiently to win her heart, mainly being there for her in a very difficult moment of her life. (from http://members.tripod.com/~aoisora)

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

Takashi Ichinomiya