Original Ideas
Idea One: A world that was brought to brink of destruction by World War 3 but was saved by the return of magic and mystical creatures to Earth. Humanity was given the ability to use 100% of their brains which allowed them to come up with some supernatural arts of their own. Most notable humans created a form of scientific magic called Alchemy but known to supernatural humans and creatures as Human Magic. This world was also given the Epic Armaments, powers and equipment that seem to take after legendary heroes and creatures from mythology. This world is in a state of calamity and change as new nations arise where the old ones fell. The current world seems to squabble amongst itself while it's larger foes creep up from their Blindspot.
Idea Two: A world severely different from our own, this world is plagued by creatures called Egnarions who are born from untimely deaths of humans. These creatures come from the corruption of those human souls who died terribly. They currently overrun North America, South America, Australia, and Antartica as well as the surrounding oceans. That leaves Humanity forced to fight with all its might to defend Asia, Europe, and Africa. But the Egnarions are also already close to overrunning Siberia know as the Eurasian Incursion zone. These Egnarions are fought by humans who are known as Espers who possess powerful souls which give them powers, Espers are from different factions which also train them in the use of specific faction techniques as well as govern the Espers.
Fandom Ideas
High School DXD AU: The way events unfolded is somewhat different from canon making the AU versions of canon characters drastically different from each other. Original characters are also welcome in this idea.
Blue Exorcist AU: An alternative universe in which Rin chose to go with Satan and became the Ninth Demon King.
D Gray Man AU: Brings the story back to the founding of the order but this time around the enemy aren't the Earl and Noah Family, nor are only Accomadators allowed to be exorcist.
Mondaiji/Problem Children: A world in which gods, demons, and like go into this realm called the Little Garden to form Communities and compete in competitions called Gift Games in which they wager their powers and equipment known as Gifts as well as sometimes resources and even people.
Berserk Band of Berserkers: Guts becomes consumed by the Berserker Armor forever becoming trapped in his form as the Beast of Darkness just like the Skull Knight was. However those two aren't the only ones to have ended up like that. As a new human takes on the Berserker Armor in order to fight against Falconia and Griffith. The other Berserkers come out of the woodwork along with some humans, magic users, and whatever else to wage war upon the God Hand.
Naturo AU: Instead of Hidden Ninja villages lands chose to use Samurai Villages instead. Basically samurai will replace ninja in the world of Naruto.
Bleach AU: The starting plot would be, beings from Hell has been amassing and absorbing the power of Hell itself. Eventually they take over Hell and even end up stealing the power of the Kushrenada. They then turn their eyes on essentially bringing Hell on Earth, Hueco Mundo, and the Soul Society. After that whole plot then the next one would be a Soul Society Civil War. I would expect a varied amount of characters including Fullbringers, Soul Reapers, Arrancar, Quincy, Kido Corps, Stealth Force, as well humans or souls who happen to possess powers or use their spirit energy in a different way.
Magi Kingdom of Magic AU: In this world there are some lore differences from the canon to make things more interesting. There are humans who naturally possess the ability to assume the form their soul had in Alma Torran. Mages are able to be added to Households but instead of metal vessel they can use a Divine Staff which gives them high level magic in the type that their household uses. This Roleplay will also explore things that weren't fleshed out like Magoi Manipulation, Dungeon Creature research, and the 8 trigrams talismans as well.