Naruto Sharingan

Shusui commited suicide but I don't think he made a pact with Itachi first. He just killed himself and Itachi (for some unknown reason) feels blame, regret and guilt. But I think Shusui actually did die and Itachi actually did do the massacre.

Itachi misinterpreted (or atleast expresses untruths about) a lot of things to do with the MS. Kakashi has it now and he isn't an Uchiha and hasn't murdered his best friend per se. But he has witnessed his best friend's death for which he has always felt blame, guilt and regret .... so I believe those factors are what are ACTUALLY the prerequisites for MS ... not the actual act of killing itself, but the way you feel blame for it.

And the Massacre is too personal for it to be a coverup for either Shusui or Akatsuki. If it was a coverup to protect Sasuke and fool him at the same time? Protect him from what? Maybe Itachi just was spared from their massacre because of his Akatsuki or Shusui involvement and happened to use the opportunity provided to save Sasuke and brainwash him? Sasuke witnessed the massacre in the Tsukoyomi state. And Itachi made sure he knew exactly who to blame. But why?

Itachi DID kill his family. It was too specific an attack for it not to have been Itachi's plan in the first place. And too personal for any Akatsuki involvement. If Shusui was doing the killing why would Sasuke have been spared? Not only does Itachi love Sasuke (unlike how he feels toward the rest of the clan) but even more pertinent, he also sees (only) Sasuke as someone worth keeping around and someone worth encouraging to grow. And ONLY Itachi (and perhaps Sasuke's parents) sees Sasuke this way. Itachi was already mixed up with Akatsuki before the massacre (which would have given Itachi the extra final motive to willingly become cutoff from Konoha) but that had no bearing on his much more personal relationship and conflict with this brother.This is the full theory that inspired the image:

I think, as weird as it seems, the massacre was actually Itachi's expression of love for Sasuke. Now, before you get all huffy, hear me out ... We know Itachi was plagued by society's limitations, arrogance and the isolation caused by genius. He was never challenged and he knows that Sasuke is probably headed down the same path. And he kills this path with the Uchiha clan. He gains the freedom and rival he craves in one blow. And why does he choose Sasuke as the rival? Not just because Sasuke has the physical ability to become as powerful as Itachi ... but I believe because by creating himself as "a wall for Sasuke to overcome, even if that means Sasuke hates him", then Sasuke never has the limitations, arrogance or isolation of being unchallenged. The Uchiha men never expressed themselves well!!!

Some believe Itachi was supposed to kill his loved ones in order to join Akatsuki, but couldn’t bring himself to kill Sasuke so he took out the entire clan instead. I like this theory even if I don’t agree. He saved Sasuke for a reason more complex than a need for a rival or brotherly love. The reason I still think my previous theory holds water is that even though others didn't see Sasuke's premature genius, didn't pressure him the same way, and treated him like the pathetic younger brother in comparison to Itachi, I think Itachi saw Sasuke differently. Itachi realized in little Sasuke's eyes was the potential for something even more powerful than Itachi to emerge. Sasuke was not isolated or limited when the massacre occurred, but Itachi realized that either that bliss wouldn't last, or, even sadder, Sasuke would remain a bud, never testing his potential. He also realized that Sasuke's hatred of him was the one thing that caused Sasuke to bloom. So - and I'm taking a leap here - If Itachi's goal is to see (In any way - including Murder, Manipulation, etc...) how far one can take the Uchiha skills - to discover how deep his "container" is - and he, out of love, wants Sasuke to flourish - then he can simultaneously attain these desires if he goads Sasuke into being the vessel that pushes those limits. Itachi sees this as the ultimate gift because he is providing Sasuke with everything he couldn't get but desperately wanted out of Konoha, but is able to reap the benefits as well.