Azumi is an innocent and average looking young high school girl. However, after moving from Kyushu to a new city and new apartment complex she meets Chizuru. At first the friendly Azumi tries to be nice to Chizuru, only to be harshly rejected. Eventually though, the two become friends, although Azumi fears that there might be something weird about Chizuru. Azumi, who wishes to become a screenwriter, one day attempts to join the drama club. There she befriends a young, amateur film maker named Ryuichi Kobayashi.

Yoshida Chizuru is the sexiest co-ed in her class. Secretly, she's been appearing in TV commercials - despite the fact that students are forbidden from working. But one of her professors has uncovered her secret and hopes to use this information to his advantage. Yoshida's got plans of her own, and has no intention of giving up her acting career...

Despite the title, Hen is NOT Hentai. It does have sex, strong language, yuri, and other elements that might make you think "Hentai". 
Chizuru Yoshida is not your typical high schooler and she's all too aware of it! She has a talent with getting what she wants from her male lovers and often comes across as cold and manipulative... 
In truth, despite her experiences with guys, she has never been in love. That's until the fateful arrival of newly-trasferred student, Azumi Yamada, at her school. It was love at first site for Chizuru--indeed an unexpected turn of events for the story's vixen! 
Not only was she in love but with all things another girl. Chizuru goes through a brief stage of anger and denial and tries to convince herself that she couldn't possibly be attracted to such a simple-looking, shy, and naive girl! To her despair she finds herself constantly thinking of Azumi, so she finally resolves to become friends with her, but it's not too long when she starts to push things along with Azumi... 
(Source: Manga Project)