At nine years old, Ren has run away from home after the sudden death of his single mother. While trying to live on the streets of Shibuya (Tokyo), he's approached by a couple of "beasts" - intelligent humanoid animals who sometimes cross into the human world. The very grumpy Kumatetsu suggests, mostly as a joke, that perhaps this child could be his student? Ren follows them, and finds himself in the land of the Beasts (where humans are very rare indeed). He begins a very contentious student-teacher relationship with Kumatetsu, in which it's not always clear who is the teacher. And he meets many other people and beasts who guide him, trouble him, and help him.
The story is heavy-handed about the lessons of trying to be overly independent when growing up (and being true to yourself, and treating people right, and ...). But as a whole, the movie is not only funny, but also deeply touching, and amazingly beautiful. I think this now ranks #3 on my list of best anime movies - it is beaten only by "Spirited Away" and "Paprika," so it's in extraordinary company. A very fine movie indeed.