In a high-class segregated society Twenty Minutes into the Future, the young genius Shion helps a convicted boy escape from the soldiers pursuing him, resulting in Shion's subsequent demotion and loss of his special privileges. Four years later, he finds himself serving in the maintenance crew of the city park, until events conspire for the two to meet again, kicking off a series of events that cause Shion to question everything he has ever been told about the city he calls home — No. 6.An anime series based on the original light novels was part of the Summer 2011 noitaminA Lineup, courtesy of Studio BONES. There is also a manga series drawn by Kino Hinoki.Oh, and do note that, despite the similarities in name, the story has nothing to witha certain Blue Submarine fleet.
After the End: Atomic warfare has left us with only six habitable city-states.
Apocalypse How: Wide-scale Class 0 at first, with only a handful of cities with modern infrastructure and quality living conditions left. Later, No. 6 experiences Gaia's Vengeance, thanks to meddling with a powerful forest entity that dishes out revenge in the form of killer bees.
The Bad Guy Wins: Shion wanted to create a vaccine to protect people from the wasps but did not make it in time. The Eldritch Abomination that created the wasps got what it wanted but in the end results in a good ending.
Berserk Button: Whatever you do, don't insult the Dogkeeper's mom. Or suggest that Nezumi become a prostitute. You will suffer endlessly.
Don't forget, never harm Nezumi. Or you'll get a bullet to the brain from Shion.
Compressed Adaptation: Nine novels squeezed into eleven episodes. For the first eight or so episodes, the series appears to be an effective Adaptation Distillation, but as the climax approaches it becomes obvious how much information had to be left out.
Luminescent Blush: When Nezumi teases Shion about his little screaming fit. Shion turns completely red in embarrassment.
Magic Music: Nezumi and Safu both hear a particular song that causes them both to collapse. It causes other strange things to happen, like causing a cave to glow and is supposed to be able to "calm" nature.
Rule of Cute: The anime has cute-ified animal-like service robots like penguins and elephants that roll around the park picking up trash. In the novels and manga, the cleaning 'bots are just ordinary, cliche robots lacking much personality.
Shoot the Hostage: In episode 10, the guard captain does this to one of his own men when Nezumi holds him hostage.
Shown Their Work: The author actually does take the trouble to write intelligent dialogue about brain synapses, basic human biology, the life cycle of hornets, etc, when the characters talk. Since, you know, this society's ranking is based on IQ, and Shion is supposed to be up there at the very top. As for the fuzzy bits, well, let's just write that off to Artistic License.
Spoiler Ending: The ending sequence shows Shion with white hair, unlike in the first two episodes and Nezumi appearing to be older than Shion, unlike in the first episode. The song lyrics are even worse, spoiling how the story ends.
Take a Third Option: Shion has a bit of a genre savvy moment and suggests this, saying if the walls around No. 6 are destroyed, there would essentially be no "them" and "us", effectively terminating the city as a separate entity. Nezumi is prompt to label this suggestion as bullpoopy.
The Cavalry: Nezumi coming to Shion's rescue in episode 2.