Fate/Grand Order Alternative (up for adoption if you want)

She come from a world where everything was the opposite. Where King Arthur rules had succeeded and the tragedy of Camlan never existed, where legendary heroes live their life till old age.
Her world only have one grail, and the only way to obtained it wasn't through a battle where the strongest stands. Instead, you had to be deem worthy by the guardians. And summoning them... Caused you your life if you are not worthy.
Amongst all the masters in her world, she was the one picked by the wizard Marshall to help an alternative world... Where its last shades of humanity was threatened by an evil version of the King of Mage to extinction.