SaiKano is a love story about the relationship between two highschool students named Shuji and Chise and their small Japanese town. When the story opens, they've just begun dating in a picturesque little town in Hokkaido, a northern island in Japan and probably the US equivalent of Montana or North Dakota. It starts with a lot of the normal awkwardness of two teenagers just starting to date and almost immediately takes a turn for the worse. The official site for the anime has a little trailer question which just about sums it up.
What do you do when the girl you love becomes a weapon of mass destruction?
Chise is a sweet, clumsy, apologetic wisp of a girl who also happens to have been turned into 'the ultimate weapon' by the Japanese Self-Defense force. That's the Japanese for you. You get the impression that crossing the moral event horizon is like playing a game of double-dutch to these guys. There's a global conflict that's breaking out for unspecified reasons and the Japanese solution is to empower a 16 year old girl with freakish bio-mechanical powers which slowly consume her over time. For some reason, the entire world has turned upon the nation of Japan (I wonder why) and Chise is their only hope for survival.
At the start of the anime she's able to keep the two parts of her life separate, going to school and dating Shuji while running off and blowing up attacking enemy forces in her spare time. This begins to change as her body is slowly consumed by the alterations which made her a weapon. She slowly begins to lose her humanity, being more of a weapon in truth than a person and Shuji is the only link keeping her from losing touch altogether. You never see the full scope of what's happening in the anime since most of the characters live in the equivalent of the boondocks, but it's heavily implied that Chise is flying around the world nuking centers of mass population as the military net closes around Japan.
The damage to the planet is pretty much irreversible as we're treated to what looks like a nuclear winter and multiple earthquakes, the last of which will rip the Earth asunder. In the midst of this happy devastation we get to follow a handful of schoolmates of Shuji and Chise as they all die one by one due to the various vagaries of war. The real kick in the balls is that almost every single person dies with either unrequited or separated love. Only a few get the benefit of dying clean as the remainder manage to choke and cough up blood to their eventual end, all the while sobbing or crying out for someone who will never come.
I actually put off watching the end to this series for a couple of weeks, figuring that the last thing I needed was something depressing while already depressed. Now that I've finished it, I think I was wrong all along. It's probably for the best that I watch the really depressing things now since it feels like I'm in an emotional dead zone anyway. You can't get any lower than low, after all.
Saikano basically ends with the destruction of the entire world. Chise attempts to save her hometown, after being talked out of simply euthanizing the entire entire population right before the end in one cleansing, apocalyptic explosion. Talk about a major mistake, but Shuji gets to pay for it. Chise only manages to save him, having given him some form of immortality so that he's the only one alive in a barren, empty, and broken world. At least he'll have plenty of time to think over all of his regrets.
And the living shall envy the dead.