Saishuu Heiki Kanojo (J-Movie) (2005)

Shuji and Chise have just started dating after Chise finally admitted her feelings for him. A week into their relationship a war breaks out and hundreds of jets start bombing their town. Shuji sees a small object flying around destroying the jets at incredible speed. When debris from a destroyed jet hits the ground and slides toward him, the small figure zooms down and destroys it. Out of the wreckage Shuji sees his girlfriend Chise with a giant gun attached to her arm. She is a cyborg, enhanced by the military to become the last defense against the enemies of Japan. Now that a war has broken out they expect her to fulfill her destiny and Shuji must decide if he can handle being in a relationship with the ultimate weapon.