The particulars are these: It's based on the five-book Japanese novel series by Hiroshi Morii, the prolific science mystery author of several similarly described series'. This appears to be the singular work to appear on film. As far as Sky Crawlers goes, it turned out to be quite an accomplishment coaxing a single film from the immense and complex literary work, much the same way Yasutaka Tsutsui's Paprika novel put Satoshi Kon & Co. to the test, requiring a leap of faith on the author's part and even more of an effort to bring to fruition the most difficult source material's spirit.
One only must be as familiar with director Mamoru Oshii's Ghost in the Shell 2: Innocence to get a general sense of the grinding intellectual prowess he brings to Sky Crawler, although, thankfully, he is a far lighter and more playful here. Where he would relentlessly pound metaphysical principles and analysis at auds in GitS2, he has become mindful that confounding and intricate ideas really can be gotten if a bit of breathing room is given. And the film is more rewarding for that. Oshii's most recognisable hallmark is also front and center in Sky Crawlers; the pet basset hound. If there is anything that will signal this is a Mamoru Oshii creation, it's that.
The gist of things are that an isolated air-base is home to a handful of so-called Kildren, children who fly reconnoissance missions and sometimes engage to protect a very specific portion of territory for an unnamed Alliance. Did I mention they don't age? They fly until they die. And if they encounter an axis pilot dubbed "The Teacher" they most certainly will. The story begins, and exists, primarily around a boy who arrives at the base with an unnatural interest in his own lost memories. Soon the history of his superior officer, a girl no older than himself, weighs on him. She knows more that she lets on and by her demeanor he begins to discover a past between them that shouldn't exist. In fact, even his fellow pilots, all three of them, are nonchalant about their boss, as well as the reasons they fly in the first place. But this is what they do and it's alright with them. Not to mention the group of adults that service their planes but maintain a removed attitude toward the Kildren.
It's really a slow-burner of a film and very confined in its scope, while at the same time offering commentary on issues from the futility of war itself to the virtue of participation and the metaphorical and actual killing of innocence, all without, as I mentioned, lecturing or flooding us with so much dialogue and theory that you want to dunk your head into a tub of ice water. But it is rewarding enough. And a visual treat to boot.