For years scientist as well as the common people have pondered the idea of awakening the dead, whether it be a child wishing back a pet, or a scientist wishing back a great mind, little do we know that a secret government organization has been attempting just that. In the year of 2036 that objective is finally completed, scientist invent a chemical that with only a drop, can revive even the most desecrated bones, but this invention is kept a secret from the public. However, one day a secret spy from the Illuminati obtains the chemical and takes it back to headquarters, where the secret society uses it to revive the leaders of the Axis powers of World War Two: Adolf Hitler, Joseph Stalin, Benito Mussolini, and Emperor Hirohito. In a turn of events the former leaders overtake the secret society, and alter the chemical to make the dead that it revives unstoppable, mindless death machines, and set out to take over the world in a mindless bloodbath, killing ANYONE they see, including children, families, babies, EVERYONE. Innocent people try to defend themselves, but the dead army was too overpowering, some people had to face deceased family and friends, and even if they managed to destroy a walking corpse, it would turn to dust at their feet. This becomes the ultimate fight of the once dead vs the living.
In a state of panic, the countries of the world put aside their differences and call upon some of the most powerful, and influential people of the time:
The benders and non-benders from the Avatar: The Last Airbender/Legend of Korra universe.
The benders/non-benders provide both air and ground defense and offense, with the Avatar leading the group, she calls upon her previous avatar spirits to come back and kick some ass. Benders take the power of the elements and multiply it 10-fold, Waterbenders plow the dead with the strength of the ocean, Airbenders send them spinning in tornadoes, Firebenders burn them in the flames of the Hells they came from, and Earthbenders pound them back into the ground for which they came. Non-Benders utilize the advanced modern technology and warfare using guns, planes, and other strength diminishing machines they can get their bloody hands on.
The Battle of Hogwart's Vets
After kicking Voldemort's army's ass in the battle of Hogwarts, the veterans - as well as their children - from the mighty battle return to put a magical twist in the Battle of the Dead. Harry, Hermoine, Ron, and all of the remaining others, as well as the new witches and wizards of the Magical world, come together and fight the muggles' battle, using the wave of their wands, the speed of their broomsticks, or their Fantastic Beasts.
After a fearsome, brutal, and crumbling battle, the alliance wins by killing the entire army as well as their leaders once again, but the post-war world proved to be just as deadly. The Battle of the Dead forced some people to fight and destroy long lost family and friends, and what once was dead, if killed again, leave nothing but dust. Once the alliance obliterated the enemy, no one had a grave to visit again, only dust in the wind. After much investigation, it was discovered that one of the primary substances used in the Revival Chemical was water from one of the rivers in the spirit world, causing the world to turn against Benders for being the reason the spirit portals are open, and authorities sent out search parties to hunt them down and end them, many of the surviving civilians from the war went on a violent rampage as well. The Avatar tried to protect the benders, but was hesitant on killing innocent people, but after her family was murdered, she went into the avatar state in rage, after a long, drawn out fight, she was killed, ending the avatar cycle. The small remaining benders, went into hiding, but were hunted down by authorities. After 2 more years, the benders went extinct. This goes to show how no matter what the good do, they don't always get the thanks they need.