Shy Chise and nervous Shuji are high school seniors in a small town and have just started dating. But everything changes when Shuji discovers that Chise has been engineered by the Japanese Self Defense Force to transform into the Ultimate Weapon! Soon Chise is torn between realizing her potential as a devastating fighting force and her desire to share a bowl of ramen with her new boyfriend!

Hoping to introduce a little bit of normalcy into their lives, Chise and her boyfriend, Shuji, flee their war-torn hometown. Hiding out in a small, out-of-the way village, the two lovebirds start living together in domestic bliss.

The couple's newfound happiness is short-lived, however. It becomes obvious pretty quickly that the fragile teenager cannot run away from her martial responsibilities. Much to Chise's horror, her body has transformed into a weapon of mass destruction--and like it or not, she must fulfill her duty to kill.