Honda Touru lost both her parents and has nowhere to live. So she puts up a tent in the forest and lives there. One day, she stumbles upon classmate Souma Yuuki's house on her way to school, who shares the house with his cousin, Souma Shigure. After getting sick and having her secret discovered by the Souma's, she stays at their house. They seem like normal people until another Souma, Kyou, shows up and challenges Yuuki to a fight. Touru accidentally hugs Kyou and he turns into a cat! Then Touru bumps into both Yuuki and Shigure and they turn into a mouse and a dog. It turns out that the Souma family has been cursed by spirits of animals, more specifically, the 12 animals of the Chinese zodiac, called the Juunishi. Touru knew that she has discovered a big secret of the Souma family but keeps it to herself. Touru continues to live with Yuuki, Kyou, and Shigure even though no one outside the Souma family is supposed to know about the secret. Touru comes into Kyou's and Yuuki's life and opens their hearts up, which have been lonely and fearful. Fruits Basket is a wonderful story about friendship and acceptance.

Anyway, here are some links to help you: this one and this one.

This anime series is complete with 26 episodes. I also have manga chapters 18-21.