@Cyborg: Overall very nice theory, well thought out, supported by the manga and presented in a clear and easy to understand way, so excellent job there in the presentation department.
Regarding the theory, as presented, I think that Itachi's gift is way too overpowered, such that it negates the MS and/or nerfs the EMS. I think it may work initially on all techniques, for example first use only, or work on only one technique initially, like Tsukiyomi when they land. Naruto in Kyuubi mode will be difficult due to his speed to line up a Tsukiyomi/Ameratsu, but Sasuke is a growing expert in these MS techniques.
I don't think it's something that's going to last the entire fight as to my knowledge Sasuke has nothing over Naruto that nullifies any of his abilities all fight long, and this would give Naruto way too much of an advantage if he's essentially fighting a 3-tomoe Sasuke, which is pre-Shippuuden. Hashirama took on Madara with the EMS and Kyuubi (until Hashirama took control and Mito sealed it inside herself), so I don't think the EMS is so deadly that it can't be fought by high level ninja without the need for some negation.
Regarding the spiritual items, I don't think Sasuke has them. It doesn't make sense to me for spiritual items like the sword of Totsuka and Yata mirror to have a basis in the physical world, namely Itachi's dead eyes, but I have no idea with Kishi. I would think that they'd randomly scattered when Itachi died, to be found again by the next person. That's just speculation, and I'm not sure how it works until Sasuke opens his eyes and goes to work. If he has them, Yata's mirror is a bigger issue than the sword to a certain extent because of Naruto's speed; however, the gift may be a spiritual item that stalemates each of the spiritual items.
I do agree that the gift is not intended to harm Sasuke, but it may bind/seal him in some fashion. For example, it may temporarily seal his eye/s, or something like that after he casts, say an Ameratsu that eye is temporarily sealed.
What I wonder is how well this gift will work with the EMS, for two reasons.
First, the EMS is naturally more powerful than the MS, so the efficacy may be diminished simply due to this, as well as the fourth doujutsu that Itachi doesn't know and couldn't have planned on a counter for.
Second, while Sasuke's EMS does use Itachi's eye's, the EMS, based on Madara's EMS, looked half like Madara's MS and half like Izuna's, so I expect the same from Sasuke's. Thus, I worry that the crow's recognition/efficacy will be diminished by this as well, but maybe that's reading the manga too strictly, not sure.
Thus, I think you're onto something, but I think a more toned down version is more realistic to expect in the manga. Overall, an interesting theory. Nice job.
Peace
dont knw if someone really noticed this or not..the eye in which MS was activated in the first picture was itachi's right eye..and the picture in whic he says lets see what happens is his left eye..lol..
Yeah, I looked that up after you mentioned it, and I only realized it based on eye shape and eyebrow dash. Sharp catch.
Peace
So long story short i think this gift is to counter that genjutsu haxed sword.
That being said itachi was very surprised that naruto can control the fox, so he probally thought naruto at the time need all the help he can get. When itachi meet naruto, naruto didnt even have sage mode.
So it could be something as simple as negate ms techs but that would be reduntant as naruto can deal with it at this stage of his growth.
Maybe, but I don't know if Sasuke even has the Totsuka sword, or what gift would even protect Naruto aside from another spiritual item, and why would that be triggered by the MS? As I said in a separate response, I find it odd that spiritual items would be stored in Itachi's eyes (a previously dead physical medium). I think they scattered when Itachi died, but Kishi may have decided to give them to Sasuke.
I do agree that Naruto in Kyuubi mode due to his speed and chakra-mode-switching can get him out of Ameratsu and Sasuke's Tsukiyomi (assuming it still lacks the temporal control Itachi's had, otherwise, 1s=72hrs, then chakra mode switching isn't fast enough.).
However, nothing is perfect, Naruto may have the ability to dodge/cancel those two MS abilities, but it doesn't mean he'll be perfect as Sasuke is no slouch, so being able to break/cancel them is valuable. Albeit I've never been worried about Tsukiyomi and Naruto. Sure it's meant to break the spirit, but Naruto has the strongest spirit of all the characters in Naruto. With the Kyuubi mode, even if Ameratsu lands, I wonder if a chakra hand can just push it off into the dirt.
Peace
He wants to see if his ''gift'' works.
Unfortunately for us, I wonder if Itachi will see just enough to decide it works before sending it back in, without us actually seeing what it does. It's either that or I think we'll get a full blown explanation.
Peace.