《枪娘》主要讲述的是失去战斗记忆的主角凯瑞寻找自我，并最终“觉醒”的故事。2025年至2030年之间，一场波及全人类的世界大战致使一半人口遭到毁灭，而人类已经无法控制战争的走向，为了夺取最后的胜利，犹如游戏般的无人战斗逐渐激化，战争已经变成：卫星镭射、无人机轰炸、智能AI、无人多炮塔坦克群之间的战场……然后，这里还有一群使用已经落后于时代的枪械进行战斗的少女——枪娘。时间回到过去。飞来地球的“智能的宇宙生命精神体”，为了躲避同类的追捕，跟附近的武器商人仓库里的“无机物”M4A1相融合。辗转之中，“M4A1”流落到某都市的军事宅少年手里，少女把“M4A1”拿回家，跟她说话，关爱她，小心的擦拭她，宇宙生命体再次开始活动。为了响应青年的感情，枪（宇宙生命体）自主的变身为美少女，青年管变为人形的枪叫“凯瑞”。然而，知道了凯瑞存在的几大国家，开始了凯瑞的捕获竞争，青年为了保护凯瑞而死去。人类开始了对“枪娘”凯瑞的研究。巴雷特、沙莎等人就是研究的推进产品，通过对凯瑞的研究，人类科技得到长足发展，进入了太空时代。 赌上宇宙圈的霸权，各大国家的世界大战爆发，“世界大战”正式展开。

Zhang Xiaoming is grandson of a Korean War hero. Due to morning reading comics peep at the same table as the captain discovered and reported teacher confiscated his red scarf. Then Zhang Xiaoming pride was badly hit, everywhere frowned upon and is considered losers. Later, he was later informed that the class teacher is a lot of red scarf, called to the playground left standing. Zhang Xiaoming coerced during the school bully, was forced to climb the flagpole, the flag fell accidentally grabbed the injured. Teacher went to the hospital for criticism and education, after Zhang Xiaoming know the father is the Secretary for Education, teacher immediately corrected himself, his father's face in front of Zhang Xiaoming praise. Later, Zhang Xiaoming is portrayed as heroic and deserving protect the flag, not only took back the red scarf, which they also won in class red flag. But Zhang Xiaoming so the state has not changed, still morning reading comic books when, at the same table again snitch captain. But this time the teacher not only did not criticize Zhang Xiaoming, a captain who actually ripped off the red scarf, saying not concentrate on reading, and accused him of slander "protect the flag guards" Zhang Xiaoming. At this time Zhang Xiaoming's face evil smile