Koharu is a quiet high school student who can’t find her place in this world.
One day, she buys a plastic model gun and a figure called “Alice” from a mysterious model shop. When she puts them together, she is sucked into a parallel world.
In this parallel world, an empty school has become a battlefield.
Nearby is Alice, the model that Koharu put together and she speaks to Koharu like a human.
People calling themselves team mates come closer and the survival game begins.
It is called “Girl Gun Fight.”
Koharu participates in the battle against the enemy team without knowing whether it’s real or a dream. When she finishes a battle, she finds herself in bed and it’s morning.
Koharu thinks it was just a bad dream, but when she goes to school, she finds out that the parallel world is held once a week and the invited members are all high school girls who have been to the strange model shop.
Who’s doing this? What’s their aim? Koharu wonders, but the survival game begins without providing any answers.
After participating in several battles, Koharu discovers the shocking truth that if you die three times in the parallel world, you die in real life. She rejects combat, but ironically finds her talent for it blossoming.
Meanwhile, a powerful warrior who is “absolute perfection” appears in the parallel world.
In real life, it’s Matsuko, the student council president and former friend of Koharu.
Koharu and Matsuko hatch a plan to escape from the parallel world.
Can the two escape from this nightmare?

在现实世界感觉无处立足的朴素女高中生・小春。
突然有一天，在不可思议的模型小店里购买了手枪模型「阿莉丝」，小春在组装模型的过程中，被召唤到另一个平行世界里。在那里的平行世界里有一个无学生的学校。
在小春的身旁组装好的阿莉丝象人类一样站在身旁，和她说话。同样被称为同学的成员也聚集过来，就这样生存游戏开始了。游戏的名字叫「枪战女孩」。

分不清到底是梦境还是现实，就参加了对敌作战的小春，在战斗结束后，在床上醒来时已经是早晨。
本以为是恶梦的小春来到学校后发现，参加每周举行一次平行世界的游戏被召唤成员，不可思议的都是去过模型小店的女高中生。
到底是谁？是什么目的？一边想着这个疑惑的小春，一边没有办法的在游戏中开始参加。
然后参加过几次战斗游戏的小春发现一个惊人事实，如果在另一个平行世界里死三次，在现实世界里其本人也会死。虽热案小春在游戏中非常拒绝战斗，但是让人讽刺的是在争斗的游戏中才华显露。
在这当中，另一个平行世界里出现了一位「从无缺席」的最强战士。在现实世界里是当学生会长的松子，也是小春曾经的好朋友。
小春向松子提出想办法从这个平行世界里逃脱出来。结果两人从这个地狱里能够逃脱出来么・・・。

It is set in a high-tech future in which humans have learned how to transfer their minds and emotions with perfect fidelity into mechanical bodies, thus achieving practical immortality. However poors who can not afford the mechanical bodies are discriminated and persecuted by mechanical people.

Tetsuro Hoshino desperately wants an indestructible machine body, giving him the ability to live forever and have the freedom that the unmechanized don't have. While machine bodies are impossibly expensive, they are supposedly given away for free in the Andromeda galaxy, the end of the line for the Galaxy Express 999, a space train that only comes to Earth once a year.

Tetsuro encounters Maetel who is a dead ringer to his mother, who was killed by Count Mecha and gang of human hunters. Maetel offers him an unlimited use pass for the 999 if he will be her traveling companion. They continue their travel through space, in search of mechanical bodies. However Tetsuro does not know that Maetel has hidden agenda...