Unicorn Catacombs

This is an idea I have as sort of a response/idea from the currently existing stories/songs of Cupcakes and Rainbow Factory.

Cupcakes is for Earth Ponies with Pinkie Pie.

Rainbow Factory is for Pegasus's with Rainbow Dash.

Unicorn Catacombes is for Unicorn's with Rarity.

The reason I chose Rarity is because of the end of season 3 she is the last Unicorn of their group, since Twilight is now an Alicorn. I chose to keep Twilight an Alicorn because I think the inner conflict and her status as no longer being a Unicorn would add to the depth of the story.

Unicorn Catacombes is the telling of how Unicorn's have magic. Why they are the ones to use it and how. Yes they do have horns, an since earth and flying are already covered by the other types of ponies, why does that inherently make them able to use magic? Why can't other ponies use magic without a horn like Discord and Zekora can? (and yes Discord does have horns but they are different to me and yes Zekora uses natural products to make potions but that's different too)

Why do Unicorn's control magic? Is it natural? Or is it created differently?

Magic in this story is created by the suffering and torture of weak and feeble Unicorn's, drawing out their natural magic (which I believe EVERY pony has, including earth and sky)  and absorbing it into crystals to share with the entire Unicorn family over many gernerations.

This to me explains why Unicorn's of they bygone era could raise and set the moon without the Alicorn's.

This story starts in the Crystal Empire where the Librarian has found an old text that she remembered King Sombra was completely obsessed with. Shining Armour and Cadence decide to ask Twilight to decipher and investigate more into King Sombra's actions before the Crystal Empire was sealed. Has anyone noticed that the entirety of the Crystal Empire has NO UNICORNS?

After Twilight has managed to decipher the text she is left with more questions than answers. The text is actually the crazed writings of King Sombra himself, but due to the detached ramblings of his writing and failing psyche, Twilight is only able to decipher this: Unicorns, Crystals and a Ritual. As well as the fact that whatever it was, not only was King Sombra both parts equally obsessed with it as well as terrified, so are the rest of the Crystal Ponies!

Twilight decides to ask for her friends help in gathering information from the residents, thought this proves to be a fruitless endeavour as all the Crystal Ponies are too traumatized to recount it.

Frustrated Twilight decides to go home for the time being and think over everything that has happened. She writes a letter to Celestia form Ponyville, wishing to keep close with her friends incase she thinks of anything. When the response she receives from her most beloved teacher dances around the matter entirely! Much like when she had first told her about the Mare in the Moon. Twilight decides there and then that she will discover the meaning of these crazed ramblings herself.