Saikano

Saikano, known in Japan as Saishū Heiki Kanojo (最終 兵器 彼女, Saishū Heiki Kanojo?, lit. "She, the Ultimate Weapon" or "My Girlfriend, the Ultimate Weapon") is a manga, anime, and OVA series by Shin Takahashi, creator of Iihito and Kimi no Kakera. Saikano was originally serialized in Shogakukan's Big Comic Spirits magazine.
A live-action movie adaptation was released in Japan on 28 January 2006 with Aki Maeda starring as Chise.[1]
Many of the locations used in Saikano can be found in Otaru-shi, west of Sapporo. The train station, "Hell's Hill", the Asahi Observation Hill, and the school all exist within the city.

Plot
The story begins with Shuji (シュウジ, Shūji?), a high school student in Hokkaidō, walking up to an observatory and reminiscing about his girlfriend, Chise (ちせ, Chise?). He finds her exchange diaries that she purposefully left behind. The whole story is narrated by him through flashbacks while reading Chise's diary. Chise, a fellow student in his class, declares her love for Shuji at the beginning of the series. However, Chise is very shy and Shuji is insensitive. Neither know how to express their feelings very well, but they do indeed have feelings for each other.
One day, while Shuji is shopping in Sapporo, unknown bombers attack the city in broad daylight. He and his friends run for cover, but notice a fast and small flying object shoot down enemy bombers. Separated from his friends, Shuji wanders through the wreckage only to stumble upon Chise. She has metal wings and weapons apparently grafted onto her body. She tells him she has become the ultimate weapon, without her knowledge or consent. However, she is seen by the Japan Self-Defense Forces (JSDF) as the last hope for defending Japan from imminent invasion by unknown foreign forces. In the anime, it is not apparent why Chise was chosen to be the ultimate weapon or why the country is under attack. It is not until the OVA episodes were released that an explanation of Chise being chosen is offered: her body had the highest degree of compatibility with the weapon system. In fact, later in the OVA it is mentioned that Chise had been "over-developed" and was so much of a weapon that she would kill anyone regardless of what side they were on. (This fact is punctuated by Chise vaporizing the Special Forces building where she first became the ultimate weapon.)
This story, as suggested by the subtitle "The Last Love Song On This Little Planet", is primarily a love story. The story focuses primarily on Chise's reactions to her increasingly powerful destructive abilities, Shuji's reaction to the same, and the relationship between the two of them.
A number of minor characters who do not necessarily know of Chise's role in the war, have sub-plots that mostly concern everyday people in the context of war: a woman whose husband is constantly away from home, a school boy who joins the army to protect his girlfriend, a girl whose civilian boyfriend was killed in a bombing, and others.

Both the manga and the anime feature a hotly-contested war. Battles are shown through the lives of people on the front, but the diplomatic particulars of the war are not revealed to the audience. A reason is never given as to why the war broke out in the first place, what the war is all about, or what countries the Japan Self-Defense Forces and Chise are fighting against. However, there is speculation about possible foes. For example, in one episode an enemy plane is shot down near the city and the pilot's one or two lines are in near perfect American English. In the manga, Chise speaks to the enemy soldiers, saying that she does not know much English, and later in the series there are certain enemy soldiers that speak French. The OVAs also portray some of the soldiers speaking French. This would suggest that there is an international coalition invading Japan.
However, in the end of both the anime and the manga, Chise remarks that many other parts of the world had experienced "horrendous things", and that "humans have done a lot of damage to this world". This may imply that the invasion was due to the lack of livable land anywhere else other than Japan, which was protected by Chise. This in turn would cause other countries to seek places where people are able to live. On the other hand, Chise could have been referring to her own creation and her part in destroying much of the world. In the manga, Chise does refer to the catalyst for the environmental doomsday, but never states anything specific until the end when she states that an earthquake will strike the core of the planet. Whether the two earthquakes that have occurred previously have anything to do with the chains of events leading to doomsday, has not been ascertained.
The only weapons of mass destruction observed in both the anime and manga was Chise herself, who by the middle of the story had the power to destroy entire cities and did so on a fairly regular basis. In more than one battle over a Japanese city, Chise simply vaporized the city and most of the people in it. Coupled with the comments about how the enemy had nowhere to return to and how Chise has been "working" all over the world, it seems unlikely that the invasion by other nations is simply over territory.
Also troubling is the seeming nonexistence of a nuclear arsenal in the invading coalition forces. No nuclear weapon is ever used against Japan, despite Japan having no nuclear arsenal of its own, and coalition forces willing to inflict civilian casualties through total war. Though an ICBM would have undoubtedly destroyed Chise in the beginning, it is never seen nor mentioned in the series. Some have argued that this is because the invading nations are desperate to capture Chise to study then destroy her for their own safety, or use her or the material she has been transformed into for their own purposes. If the latter is correct, and if the other nations were aware of the inevitable doomsday scenario mentioned by Japan's leaders, then the act of capturing Chise would possibly be seen as the only way to save their own respective nation. Chise, in fact, does reach a point of power where she is able to synthesize voluminous pieces of matter out of thin air, but it is dubious whether or not Japan would have been able to have saved itself, seeing as even Chise was unable to use these structures to stop an enormous tidal wave from annihilating her hometown.