Natsume is a quiet boy who was orphaned at a young age. He has a secret: he can see spirits. As a young boy, he didn't try to hide his ability, which made his foster parents think he was creepy -- and so he moved from distant relative to distant relative. He hasn't much connection to the people around him: a real loner.
However, now he moves to a small town where his grandmother Reiko used to live. She died recently, and Natsume came into possession of her belongings, one of which is a book with page upon page of caligraphy -- seemingly weird names. This turns out to be Reiko's "Book of Friends": she could see spirits too, and instead of hiding her ability, she battled the spirits and forced them to write their names into her book. This powerful spell obligated the spirits to do her bidding.
Natsume's similarity to Reiko gets him in all sorts of trouble: the spirits mistake him for Reiko, and hunt him down in order to get their names back! It is only after the spirit Nyanko (a huge white wolf-like thing) explains this to Natsume that he knows the worth of it. And obviously, the holder of the book has tremendous power over all the spirits in the area, which is why Natsume is also targetted by spirits whose names aren't in the Book too!
Nyanko turns himself into a fat cat (he had been sealed away in the image of a maneki neko) and starts to live with Natsume -- he protects him, but when Natsume turns old, Nyako says he'll eat him and take the Book of Friends for himself. And while he doesn't want to show it, he warms up to the fearless awkward boy as Natsume resolves to return the names to their rightful owners.
The difference between Reiko and Natsume is that the latter has genuine compassion for the spirits his grandmother trapped. We get to see flashbacks from when Reiko defeated the spirit -- sometimes she pulled quite a rotten trick on them.
But Natsume also spends lots of time with humans -- mostly his foster parents and his classmates. He somehow fits in, and his 'weirdness' slowly gets accepted. He even helps out some of his schoolmates with spiritual problems they have. It is very interesting to see Natsume slowly carving out his own space and settling down in this small-town village, but there are some moments of comedy as well.
The series uses a washed-out color palette that makes it seem like you're watching a moving watercolor painting -- that somehow goes very well with the nostalgic and small-town feel of the series. The character designs are not much special, but the spirits appear in a bewildering variety of forms and shapes -- and not two are the same. That's pretty interesting.
The voice acting is very good. Natsume has the slow and thoughtful voice of a boy who always watches what he says (apart from the moments when he and Nyanko-sensei are alone in his room and Natsume can tease him without being overheard).
- Really interesting look on the spirit world;
- Lots of subtle character development;
- Great nostalgic look and feel.
- Slow moving.
All in all, a very enjoyable view. I'll give it a solid 8.5.