Set in an alternate Earth in the mid twentieth century, Strike Witches tells the story of a fight to protect the world using a combination of magic and technology in a fictional recreation of events occurring in World War II with the national armies joining forces to confront an overwhelming alien threat together instead of fighting among themselves.
The titular Strike Witches are young women with high magical potential who are recruited into military organizations around the world to fight against the enigmatic Neuroi, which began an invasion of unprecedented scale on human territory in the year 1939. This puzzling enemy force has appeared frequently and without warning in many areas across the world throughout history. The weapons of the Neuroi mostly take on forms similar to aircraft, but their most troubling tactic is the spreading of a corrosive miasma. Not only do normal humans have no defense against this miasma, but the remnants of the land affected by it are processed by the Neuroi into new weapons, crumbling huge sections of former nations into the sea. As the miasma seems to be unable to spread across large bodies of water, humanity has designated such areas as their main lines of defense.
In order to bring out their potential for use in battle, each Witch equips a unique machine onto their legs: the Striker Unit. With the Striker Unit equipped, they gain the ability to fly and their tapped magical potential provides the strength to utilize weapons far too heavy and powerful for a normal person. A defensive field is also created that can protect the Witches from the Neuroi's miasma, as well as other physical weaponry, making them humanity's trump card in the war.

Strike witches have also ability and appearance changes, such as

Magic
Magic is a natural ability unique to Witches which manifests as a blue aura followed by the appearance of animal ears and tails. Magic is stated to be divided into two categories telepathic/clairvoyant and telekinetic and are treated as a natural force of energy subject to the laws of physics. Although physically taxing, control and technique can improve the expenditure of energy. Magic can be used for such things as healing, vastly enhancing strength and vision, and for stabilizing and enhancing weapons such as guns and swords. They can even be used to survive in hostile environments such as the vacuum of space and from radiation. In battle, their most common uses are powering the Striker Units and forming defensive shields. Magic can freely interact with technology and as such can be strengthened through technological means and even hijacked by the Neuroi.


Deflector Shield
An ability universal to all Witches is the ability to raise runic energy shields for protection. Shields are consciously activated but instinctive in nature able to block multiple attacks coming from all directions and even protect Witches from crashing into objects. Each shield bears different glyphs depending on the nationality of the Witch i.e. Fuso Witches have Japanese characters etc.


Witch
A female user of magic. Male users do not appear to exist in any of the media (though a mecha intended to supplant the Strike Witches is named "Warlock", or male magic user). It has been suggested by the novels that male Witches do exist but are rarer and likely much weaker hence their absence in the Witch corps contrasting the universal male presence in the standard armed forces.


Familiar
An animal spirit which binds to a Witch increasing their innate magical power as well as grant unique abilities. For instance rabbit familiars are known to grant super-hearing while cat familiars can grant night-vision. They are outwardly visible by their ears and tails on the witches they merge with when manifesting magic. Familiars are able to manifest entirely and even act independently but rarely do so. Familiars are either absent entirely or not emphasized in the anime.


Striker Unit (Air)
A pair of hybrid mechanical/magical propeller devices used by Witches for flight and worn over their legs. They are rigid, preventing movement of the knees, but can be disengaged on the field if needed. When wearing a Striker a Witch's power is vastly increased by a magic engine in the unit, resulting in the constant manifestation of their animal ears and tails. It grants them the power of high speed flight. Strikers require high magical aptitude however and Witches who are either too weak or past their prime cannot use them effectively. Each character's Striker is designed to resemble a type of World War II fighter plane. While most Air Strikers are based on propeller driven, rotor-craft, there have been a few prototypes of Jet propelled Striker Units built by Karlsland. While faster, more maneuverable and capable of flying at higher altitudes it has been noted that the prototype jet strikers burn trough more magical energy compared to Propeller driven Strikers.


Striker Unit (Land)
The tank equivalent to Air Strikers. Land Strikers resemble the caterpillar treads of tanks and even allow Witches to travel at high ground speeds via a sliding motion. Note the treads are located in the lower leg sections and spin along the shins and calves; no physical contact is made with the ground instead a magical field propels the Witch. Because magic is subjected to the laws of physics large amounts of magic is used like fuel to maintain flight in Air Strikers. Land Strikers by contrast don't have this problem and can instead focus all their magic into their shields making them more durable like tanks. While Land Strikers are usually propelled by using the magic propulsion field, sometimes a land witch can walk in these strikers normally without the aid of magic to propel them, hypothetically to conserve a witches energy. While most Land Striker designs are a simple, small sized units that fits over a witches legs, there have been a few Land Strikers that were built that are much larger, and are more akin to a type of Power Armor and use large caliber magic enhanced weaponry.


Wearing Striker Units
To wear a Striker Unit the Witch inserts her legs into the devices. The receiver ports are actually pocket dimension devices and require near to total skin contact to operate properly (or even fit in for that matter) as such no active Witch wears trousers as they would take too long to remove due to the erratic and often sudden nature of Neuroi attacks. Entering a Striker Unit takes only a split second. Adolfine Galland is the only known Witch to wear trousers, but she has long gone past her prime and has been promoted to the rank of Air Vice-Marshal. This serves as one of the primary vehicles of the show's fan service. Consequently since the Witches primarily wear the uniforms of their countries' armed forces most of which were meant for men (and the establishment of Witch forces was sudden and unconventional at best restricting new uniform redesigns) many of them don't even wear skirts or anything to cover their lower bodies with exception. Some Fuso (Japanese) witches wear short Hakama instead of Navy or Army uniforms while others have sufficiently large shirts or jackets or simply wear pantyhose. Of note however is the fact that this style while technical in origin has become a very popular and very common fashion trend among civilians due to the fame and respect accorded to the Witches. Consequently many young civilian women are shown to also not wear skirts or trousers but no one not even men find this in any way strange. This is comparable to the development of the bikini during this time period. As a result any social problems this might have caused at first have since become moot by the time the series begins hence why Witches are rarely seen wearing lower body clothing even when off duty.


Magic Engine
According to supplementary material the magic engine appeared alongside the steam engine utilizing steam technology to enhance magical power. The current magic engine was invented by Dr. Miyafuji and utilizes an internal combustion engine. Of note is the existence of stand alone magic engines that do not require a Witch to be immediately present one of which was used to power a human built Neuroi enhanced battleship.


Witches' Base
The 501st's first personal base of operations was in Britannian territory. It is an ornate castle that resembles Mont Saint-Michel, located on a small island jutting into the Strait of Dover near Folkestone. Its proximity to the Gallian coast makes it a strategic staging point for the Witches to quickly engage threats coming from the Neuroi-occupied European mainland. The second base they utilized was an ancient stronghold of Witches near Rome. Its most prominent features was an angel statue resembling the one in Ponte Sant'Angelo and what appears to be a Colosseum.


Neuroi
The primary antagonists of the series. They are mysterious alien entities composed of black honeycomb structure material harvested from conquered territory. Their intentions or origins are unknown however they display high levels of intelligence and are capable to adapting their weapon designs and tactics regularly. They come in various sizes from small to gigantic; capable of self-sustained flight, rapid repair, and armed with directed energy weapons. Durable self-repairing Neuroi have special multi-faceted gems within them called Cores as their power sources and only Achilles' Heel. Neuroi can be defeated by conventional forces albeit at great difficulty as their durability and firepower vastly exceed the technology of human forces. Exacerbating the problem is their ability to produce a corrosive miasma which can corrupt human machinery turning them into more Neuroi. Only over water (lacking in landmass) is the miasma neutralized however naval vessels lack the maneuverability to avoid the beam weaponry of the highly durable battleship sized Neuroi usually deployed over water making ships equally outmatched. Only Witches with their shields, high agility and magically enhanced weaponry can defeat them without incurring massive casualties. The Neuroi's designs, like many other elements in the series, have a historical basis in that they are modeled after experimental aircraft from the World War II era. Land based Neuroi are shown and seem to take the shape of armored vehicles or walker type shapes. One such land Neuroi, a Super Heavy Land Type, consisted of an assimilated Ship Hull.


Human-Form and Humanoid Neuroi
Aside from the common vehicle form Neuroi, there have also been sightings of less common human-form Neuroi, that look reminiscent of a Witch. These Neuroi in particular are even more mysterious then normal Neuroi, and their intentions or function are unknown as in the past there have been instances of such rare Neuroi using mind control on witches in battle for espionage on the enemy, but more recent examples have attempted peaceful contact with humanity and the witches. It is believed that a sort of Neuroi pre-formbecomes a human form Neuroi when it makes contact with a witch and there is no apparent hostility from the witch in question. Human Form Neuroi often appear as a grey/black witch with black skin, the animal ears and tail of a Manx cat, and have jet-like legs. They can fire lasers from both their hands and the wings of their jet legs, and their cores are located in their chest. Human-Form Neuroi are almost exactly as powerful as the witches they mimic. However, they lack the experience of witches and their capability for teamwork, so these Neuroi are no match for an experienced wing of witches. Humanoid Neuroi are a strange blend of the Human-Form Neuroi and the Aircraft type Neuroi, though how such Neuroi come to be is as of yet a mystery.


Neuroi Hive
Strongholds of local Neuroi presences they resemble giant conical funnels of swirling black clouds the size of mountains. Because Neuroi cannot move over water they mostly remain stationary over major human settlements where they slowly harvest the landscape to make weapons.