In this world, Sensha-do (戦車道), the art of tank-combat, is a traditional Japanese martial art for girls. Miho, a girl who just transferred into the Ōrai Girls' Academy in Ibaraki Prefecture, has been ordered by the academy's student council chairperson to join the school team and compete in the national Sensha-do championships.

History is coming to an end. When humans came down from the sky they brought with them the Testament, the guide to the path they must follow if they wish to return to the skies again.

Living by the sea, protecting the sea, and journeying across the sea... They're the Blue Mermaids! Because of a shift in tectonic plates around 100 years ago, Japan lost much of its area to submergence. To preserve Japan's territories, coastal cities sprung up, one after the other. Eventually, they became marine cities, and along with the expansion of sea-lanes to connect them, the need arose for a sizable staff to protect the seas. At the same time, maritime jobs were becoming more popular among women. Hence, the Blue Mermaids, tasked with keeping the seas safe, had become every female student's dream job. This is when childhood friends Akeno Misaki and Moeka China enroll in a marine high school in Yokosuka, along with other girls who share their goal of becoming a Blue Mermaid.

The year is 1939 - it was then that the Neuroi appeared. Nobody knows where they came from or what their ultimate agenda is, but the fact remains that their attacks drove people out of their towns and cities. In order to take arms against them, humanity develops a new anti-Neuroi weapon called the "Striker Unit." Using the power of magic to fight against the monsters, this new device enhances and amplifies the power of female magic-wielders. To use this device, young witches from all over the world have been brought together to form an elite task force unit called the 501st Joint Fighter Wing, commonly known as the "Strike Witches."

The year is 1939 - it was then that the Neuroi appeared. Nobody knows where they came from or what their ultimate agenda is, but the fact remains that their attacks drove people out of their towns and cities. In order to take arms against them, humanity develops a new anti-Neuroi weapon called the "Striker Unit." Using the power of magic to fight against the monsters, this new device enhances and amplifies the power of female magic-wielders. To use this device, young witches from all over the world have been brought together to form an elite task force unit called the 501st Joint Fighter Wing, commonly known as the "Strike Witches."

After discovering that the Neuroi are capable of communication with humans and making peace with the nest above Gallia, the Witches squads are on a mission to reestablish communication, when a sudden attack causes the Neuroi to vanish. The Witches discover a new and massive nest that just appeared, covering almost all Europe. Ruthlessly and without mercy it annihilates allied forces along with Witches. Word of the attack reaches Fuso and a support battalion is deployed to rescue the survivors. Among the rescue team is the former Striker captain Mio Sakamoto and the now civilian Yoshika Miyafuji, who want to save their dear friends.