The story begins with Shuji, a high school student in Hokkaido, walking up to an observatory and reminiscing about his girlfriend, 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.

The story begins with Shuji, a high school student in Hokkaido, walking up to an observatory and reminiscing about his girlfriend, 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. [ Contract ]