Saikano, a.k.a. Saishuu Heiki Kanojo; She, the Ultimate Weapon; My Girlfriend, the Ultimate Weapon. In the French translation, Larme Ultime, a pun on "the ultimate weapon" (l'arme ultime) and "ultimate tear".The tentative budding relationship between petite Chise and bitter, emotionally distant Shuuji becomes a little more complicated when Shuuji discovers that Chise has been converted into a living weapon of mass destruction by the JSDF.Originally a manga series by Shin Takahashi, it was adapted into a 13-episode anime in 2002. An OVA side-story was released in 2005, Saikano: Another Love Song, as well as a live-action movie in 2006. All of these, apart from the live-action film, are licensed by Viz Media.
Shuji's fate in the anime is to walk an empty earth, with nothing at his side but an Ax-Crazyenergy being who "loves" him too much to end his suffering. It's strongly implied that said energy being gave him immortality, which makes the situation much worse.
Subverted in the manga. Shuji and Chise somehow leave the Earth in Chise, who has become some kind of spaceship....but Chise forgot humans need to eat.
Black Comedy — Along with Gallows Humor below, there's a sequence in the manga where after Chise and Shuji run away and start hitchhiking, they eventually get picked up by a military truck. Chise says off-handedly that everyone that knows what she actually is is already dead. The punch line to this is that the soldiers on the truck DO recognize Chise and know what she is and have a collective Oh Crap in their thought bubbles.
Humans Are Bastards — Not played entirely straight, but the show makes it clear that everyone is guilty to some extent. At the same time, some passages sing the beauty of human life and the merit of committing to memory the fact that humans existed.
Pet the Dog — Chise and Shuuji love kitties. They die horribly.
Plot Hole — Could be said to be voluntary. The fact that we never learn who's at war with whom and the identity of the Big Bad strengthens the status of Saikano as an allegory about war at large. Similarly, knowing how come Chise is chosen to become the ultimate weapon and how on earth that actually works isn't quite the point. See The Unreveal.
Poor Communication Kills — Double subversion we learn fairly early on that some soldiers speak English. Then Tetsu meets up with soldiers and tries to talk them down in English. They don't understand English.
Rape as Drama — In a recent volume of canon stories happening in the universe of Saikano, one story focuses on the relationship between a teen soldier and a girl who got raped by soldiers from the other side. Particularly jarring since he waited for them to be finished before he killed them because he knew they'd feel 'spent' after sex. And since they supposedly fall in love he convinces the girl to have sex with him while she doesn't want to.
Rule of Cool — Let's face it, a moe with tech wings is cool.
Schrödinger's Cat — In the manga, one of Shuji's friends goes deaf during the first bombing. In the anime, said friend bites it (though from how little he gets featured in the manga, he might as well have died).
Seinen — In the small Afterward in the manga, Word of God stated this was for young adult boys to adult men. This is also how he got away with including a rather graphic sex sequence.
The Unreveal — For example, why and how was Chise chosen as the ultimate weapon? What actually happens to the earth at the end?
The second bit isn't outright stated, but pretty much made obvious. The Earth will eventually die, and Shuji is confined to a Fate Worse than Death due to energy-being Chise's "kindness".
The best we get for the former in one of the OVA's is she, and only she, just so happened to fit the criteria to be the ultimate weapon. It's even mentioned that it could've been anyone and they would've used him/her.