Guinevere, Queen to King Arthur in Western legend, was condemned by public opinion for her affair with Lancelot and eventually became a nun...
Niya transmigrates once more, this time to medieval England, to the age of King Arthur. But it isn't the historical age of King Arthur: it's the age of King Arthur from Fate. Then she realizes something: she seems to have taken the place of the Guinevere from history...
This is a bit of imaginative worldbuilding to fill in the gaps in Fate's age of King Arthur. It's a passion project, so it won't be very long, and updates will be irregular.