Part/Book 1 of Twilight Uchiha: Senya.

On hiatus until I get inspired again.

If a unicorn is put through too much stress, their horns begin to cast at random. Sometimes, it's as little as a levitation spell. This isn't one of those times. It's the worst case scenario of being teleported into another dimension, and the mind being nearly wiped clean, save for some images. Nothing solid. And guess who it happened to? None other than Twilight Sparkle.

To 'Madara, this presents an opportunity to spread the Uchiha genes elsewhere. But, he can't watch over her until Celestia arrives to pick her up. So, using his negotiation skills, he convinces Itachi to watch over her, as her big brother and student.(Because, let's face it. If Itachi was a parent at 13...) He accepts, and notices a likeness to a character in a book he read, and keeps on him, during and after the Third Great Ninja War.

To Itachi, this means he can try to have a better relationship with a sibling, and have someone to tell everything to. He knows she'll leave one day, but until that day comes, he'll watch over her like he would Sasuke.

Basically? In lay mans terms? Twilight in the Ninja World, being watched over by Itachi after Obito implanted her with a sharingan and some Uchiha DNA. Not a lot.