Fruits Basket

Tohru Honda has been living in a tent since her mother dies in a car accident, but ends up living instead with Yuki Sohma, her school's "prince", along with his relatives Shigure and Kyo. But Tohru soon discovers that the Sohma clan has a secret of it's own: certain members of the family are possessed by the animals of the Zodiac, so whenever they are hugged by a member of the opposite sex they turn into that animal! Tohru promises to keep their secret and vows to somehow break the curse, and she may just end up healing the Sohma clan members in other ways as well...
From Baka-Updates:
Tohru Honda, an orphaned high school girl, is taken in by the wealthy Shigure Sohma when he realizes she has nowhere else to go. However, the Sohma family shares a secret, and it isn't long before Tohru discovers that there's a reason why her classmates, Yuki and Kyo Sohma, never let girls get near them, and never talk about their lives before they lived with Shigure. And before she knows it, Tohru has become so tangled up in the lives of each member of the Sohma family that she couldn't leave even if she wanted to.
As she learns more and more about the truth of the Sohma family and the nature of their secrets, she desperately searches for a way that she can save them. But what can one girl do, especially when it seems that she may have been part of someone's plan all along . . .
Fruits Basket received the 2001 Kodansha Manga Award in the sh?jo manga category and the "Best Manga" award at the 2007 American Anime Awards.