Disclaimer: I don't own Naruto or any of the characters therein.
A/N: Warning! ShiIta. As in ShisuixItachi. You know what that means. Don't like, don't read. Thank you, and please enjoy!
..Because
Itachi wasn't invincible; possibly no one knew that better than Shisui.
It was rare, but on occasion the two would be partnered for some important mission or another-they were the Uchiha prodigies, after all, and they worked together brilliantly. At times like those it was as if they could read each other's minds; that was a product, many assumed, of growing up so close.
It was even rarer, but on occasion Shisui would have to step in and keep his cousin from being killed by an overly zealous enemy. Itachi was good-better than good-but nobody could watch their back all the time. Every so often even the great Genius Uchiha slipped up, and when that happened, Shisui made sure he was there to ensure that that one mistake didn't cost Itachi his life.
In the aftermath of such once-in-a-purple-moon events, two times out of three both boys would walk away mostly unscathed. The rest of the time-which admittedly wasn't much-Shisui would find himself in a hospital bed thanks to the dreadfully small amount of time one is given to defend in such unexpected situations. The actual damage varied-a few broken limbs here, a hole through the side there-but it was never pleasant. And such wounds took time even for medical ninja.
Times like those, a strange ritual of sorts would pass between Itachi and Shisui. It became rather unnecessary as time passed, but they carried it out nonetheless. It was almost involuntary.
Standing at his best friend's bedside, after examining the full extent of Shisui's injuries for himself, Itachi would look up with an unreadable glint in his eyes and ask why Shisui went so far for him.
The answer-which was accompanied by a playful shove, or a roll of the eyes, or a smile, depending on Shisui's mood and physical state-was always the same.
"Because I love you, you idiot."
..Owari