They both deal with school life and first love, but in their own manner. Not so descent and really unique plot follows few middle-schoolers through their every day boring life. But it also features their encounters with supernatural. Though supernatural here is also of a "slice of life" kind. No one makes a fuss about special abilities that posses main characters, no one asks them to save the Earth or change this world. Those supernatural powers showed as a very part of our everyday life. Thus main characters both in Kamichu and Windy Tales are still ordinary middle-schoolers, even though they possess some super powers.
Windy Tales and Kamichu! are all about the wonders of youth. They accent the youthful theme with a modern, real life setting that is touched with just a little bit of whimsical magic. Both are light hearted and episodic. If you've acquired a taste for magical, middle school slice of life anime, both Windy Tales and Kamichu! are right up your alley.
Although there a some big differenz between this both, for example one of them is a movie and the other one are more episodes. I think that both have somehow a touch of the feeling to adventure something new and find little things that can be interesting. They both develop with the time, learn much about all what they see and experience some wunderful situations. Also I've got those innocent child-life-feeling by both animes what I so appreciate. By the way, some magic is found in both and both have cats who takes a part in the story.
Both are brilliant 'slice of life's to relax to. They have the same eerie feel to them, and done in a similar style whereby you follow a girl's journey through everyday life taking pictures and generally finding themselves and the little enjoyments of life. Fuujin Monogatari has a tiny bit more action and an element of fantasy whilst Tamayura is a bit more toned down.
For the few that enjoyed the incredible atmosphere of Zettai Shounen, you may enjoy Windy Tales. It has a very similar atmosphere at times, though it is more evident in certain episodes. For those that enjoyed the atmosphere of Windy Tales, you may be able to appreciate Zettai Shounen. Both are beautiful series.