Simoun

Simoun is a 2006 anime made by Studio Deen and directed by Junji Nishimura. It takes place on the planet Daikariu, a world in which everyone is biologically born female. When they reach the age of seventeen, the denizens of this world embark on a pilgrimage to a holy spring, where they are given the opportunity to either stay female or become male. One of the nations of this world, the theocracy Simulacrum, has grown to prosperity thanks to its monopoly on the advanced helical technology. As a consequence of this, Simulacrum is under attack by the allied forces of the nations Argentum and Plumbum, both of which wants to steal this technology for their own uses. Simulacrum is defended by priestesses known as Sibyllae, who flies into battle in advanced airships called Simoun. The anime follows one fleet of Simoun; Chor Tempest, as its members deal with the war as well as their relationship with each other.

Simoun's biggest asset is without a doubt its cast of characters. The members of Chor Tempest all have distinct personalities, their quirks and foibles are portrayed well and they are, all in all, easy to get attached to. I think my favorite character was Mamiina, she starts out as a pretty dislikable character, but even then I thought she was interesting. Her resentment towards Rodoraemon and her willingness to do whatever it took to get ahead while not justified, are at least somewhat understandable once her backstory comes to light. Point is, Mamiina is not a jerk just for the sake of being a jerk and as the show progresses, Mamiina's more positive traits becomes more and more apparent and she ends up being what is probably Simoun's most empathetic character. That said, I could easily have picked Neviril, or Rodoraemon or Paraietta as my favorite. As I said, the characterization on this show is very good.

On the visual side of things, Simoun may not be as exciting as some other anime I've seen, but I still thought the visuals were good: I found the aerial-sequences to be thrilling and the character-designs appealing. As for the soundtrack, its of a consistently high quality, with the music reflecting the mood of what's happening very well.
If I have any criticisms against Simoun, I guess it would be that the actual plot evolving the war is not quite as interesting as the characters or the setting of the show. Don't get me wrong, the plot isn't bad or anything, but its not exactly amazing either.

Some of the characters who are identified as male are clearly voiced by women. I think I understand the reason for this, but it was still pretty distracting at first.
A word of warning: There's a lot of kissing going on in Simoun. So, if you have a problem with that, I wouldn't recommend watching the show.

To the rest of you, though, Simoun comes warmly recommended. If I ever do an expanded version of my Top Animated Shows list, it'd definitely be on it somewhere.