EDIT: ...my sister died weeks ago, I'm taking a break from everything and I pretty much forgot about this and the other story... I'm handing this account to a friend of mine... I don't know when I'm coming back to this... but stories from this account are now my friend's stories.
Months after the defeat of Sombra, they find a secret cavern underneath the kingdom. Inside the cavern is a strange statue of a bipedal being with a crown of strange deer-like antlers that was chained and tied to a corrupted crystal. Discord seems distressed and elated, the Celestial Sisters are trying to remember.
In the meanwhile....
I wanna be the very best, like no one ever waaaas~!... It's so boring, where's little Sommy? Wait... Is that...? Dissy?! Oh heeeeey, little Sunny and Moony's all grown up, awww~!... Wait... How long was I stuck in this?... God I miss my sis... Dissy? Wait No puT THAT AWAY FROM MEEE DIIIISSYYYYYYY!!!!
*CRACK BOOM*
A pair of twins attend a convention cosplaying together in a theme. Buying from a shady merchant from a strange stand causes them to split up. Sent to two different dimensions they make their own paths. Join one of the twins who turns into a human version of the Legendary Pokemon Xerneas and is capable of so much more!