From the introduction:
Welcome to the year 1939
The Great Depression is in full effect, the Nazi party is in control of the German public, and an alien race is invading earth.
World War 2 will have to wait, as these ravenous creatures called NEUROI, who consume and destroy everything they touch, threaten to drive humanity to extinction. They have already taken Germany, and are quickly pushing into France, Russia and Austria.
However this common enemy has drawn all the forces of humanity together in an effort to drive them back. And the key to this defence are Witches, women with magical powers that use their powers to defend humanity.
With mundane aviation technology devices known as Striker Units have been developed to take a Witches fight to the skies. Often described as next generation broomsticks, these devices fit over a Witch's leg and allow for areal feats impossible in a normal fighter. Not only do Striker Units allow a witch to fly but also improve their other magical abilities, allowing for greater control and precision when casting.
They women who fly Strikers are known as: STRIKE Strike Witches.