Madoka Magica: Witchswap AU
I've been sitting on this idea for too long with nothing material to show for it, so I might as well speak it into the world so somebody else can enjoy it and maybe make it themselves:
PMMM Witchswap AU: An alternate universe where all the Magical Girls encountered in the series are Witches by the start, and all the Witches encountered in the series are Magical Girls by the start.
So, instead of Mami, Kyoko, and Sayaka, you have Candeloro, Ophelia, and Oktavia. Instead of Charlotte or Uhrmann, you have Nagisa and Inui Itsumi. So on and so forth.
In my head, I like to think that the focus of a Mitakihara-set Witchswap story could be that the girls all learn about a very special Witch that is incubating somewhere in the city, its Grief Seed waiting to hatch (like Charlotte's in Episode 3): Kriemhild Gretchen. Kyubey surmises that Kriemhild's Grief Seed is uniquely capable of holding an effectively infinite amount of Soul Gem impurity, and so any Magical Girl that obtains it would never have to fight Witches again, allowing them to return to a normal life.
Thus begins a race against both the clock before Kriemhild Gretchen hatches & destroys the world in just a few days, and against all the other Magical Girls hunting for the same treasure.
Naturally, a theoretically infinite recharge Grief Seed would be able to give all of these Magical Girls normal lives, but only if they trust each other enough to share. But if they think any one of them might whisk it away for themselves, then that motivates them to just keep it for themself instead. It's a self-fulfilling thing.
Not to mention the girls would have to decide between trying to defeat Gretchen and keeping the Grief Seed, or giving it straight to Kyubey before it hatches so as to ensure the world won't be destroyed.
I like to think that Kriemhild Gretchen's Familiars would be able to leave her still-forming Labyrinth and they'd be found in the Labyrinths of the rest of the Holy Quintet's Witches. If a Magical Girl encounters these Familiars, they'd be able to track their magical signature and be better equipped to search for & find Kriemhild Gretchen's Grief Seed.
(I suppose an infinite recharge Grief Seed could also fit Shitori Egumo/Embryo Eve/Ui Tamaki, but I like to think that in a Magia Record Witchswap AU, Ui is fine and it's Iroha that becomes a Witch instead).
