Twilight Sparkle: Princess of Friendship and Magic gets called to the last place you would expect to find a friendship problem, the Canterlot Caves. Called with naught but herself and Spike she finds quite the ancient discovery but even as she gets called off to other missions this one never seems to close. What she finds is a volatile oddity with no reason for it's already puzzling existence. Somehow, it knows events that happened hundreds of years ago and shows little confusion at the new era. It still uses glyphs but can cast advanced spells without so much as a trigger word. Somehow. There's the hint of something more beyond her mask. Like she's constantly trying to plug a dam with her hooves.

The cannon has been changed slightly in an attempt to kind of 'fix' some things. Just stuff I always found stupid and some more fleshed out characters if they need it. I also added some things about characters we don't know all that much about in the show ie. Celestia but the personality remains the same.
the sex tag is implicit. Sorry.
If you notice something's off tell me, I'm still not that great at all this.
I don't really know how dark I'm going to go but if I do I'll update the tags so fear not.
obligatory 'may contain scenes too intense for young children' warning here anyways
not too edgy tho.