From MangaProject:
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 href='http://fate.tainted-reverie.net/' onclick="window.open(this.href, '_blank'); return false;">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...