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Based on this, you can see Sasuke staring at A with his hands in an apparent hand seal gesture. From this people can deduce that Sasuke has attempted some form of Sharingan Genjutsu on the Raikage. This is evident by Shi's explanation of A's fast synapses, further strengthening this argument is the Raikage's contemptuous exclamation concerning the Sharingan.
Genjutsu Susceptibility
I'll structure my counter-argument with rebuttals to the points covered, and then move onto additional arguments against the Genjutsu immunity argument.
The first point I would like to raise is that Sharingan Genjutsu doesn't require hand seals, nor has Sasuke's ever done any Genjutsu through this method. Therefore I fail to see how this provides any evidence, as there is no proof that hand seals are even a prerequisite.
The other point commonly raised is that Sasuke is attempting Genjutsu. However it is out of character for Sasuke to attempt Genjutsu at the start of a fight. Sasuke typically falls back to Genjutsu when his Ninjutsu and Kenjutsu fail, presumably due to greater comfort/skill with them. This pattern is repeated numerous times, against Orochimaru, Deidara and Killer Bee. In fact, during the entire Kage Summit arc, Sasuke's only confirmed use of Genjutsu was against Shi.
Lastly, people normally conclude from the Raikage's statement that Sasuke attempted Genjutsu that A shrugged off. However this is speculation at best, and weakened by its supporting arguments -Sharingan hand seals and out of character behaviour- also being highly speculative and unlikely as well. In addition, we see
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and
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, that A's dialogue can be linked to his general disposition at the time. By this, I mean that the context of these statements are an angry, rash man who believes he is facing his brothers kidnappers. Because of this, A proves to be contemptuous of Sasuke throughout their fight. Due to this, there seems to be nothing special about the Raikage's demeanour towards the Sharingan.
Another point I would like to raise is Kishimoto's convention when it comes to new abilities and techniques. Throughout the Manga Kishimoto uses either thought, or character to commentary to highlight what just happened. The only occurrence of this particular even if Shi's comment, already provided. However, this comment is only on A's 'fast synapses', and in no ways references an ability to resist Genjutsu through them. Such silence is reflected throughout the event; Karin is surprised, Sasuke apparently doesn't notice his Genjutsu failing, he certainly doesn't seem to care either way etc. Based on this dearth of information, the only conclusion can be that there was no Genjutsu attempted.
Nicely emphasising this point is how failing Genjutsu or techniques are normally portrayed in the manga. When Itachi's Tsukiyomi was broken, we were treated to
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. Kakashi's Shadow Clone defeating Genjutsu resulted in this
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. Likewise, when Naruto was pulled out of Itachi's Ephemeral,
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. Finally, Sakura's resistance to Ino Yamanaka's technique
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.. All this shows ample proof that when techniques fail, it is highly visible and obvious to those involved. It takes more then an angry shout to break Genjutsu. With every other method of Genjutsu breaking requiring such, it seems unlikely that 'fast synapses' is unnoticeable as a counter.
Nicely emphasizing my previous point is just how 'showy' Sasuke's Genjutsu is. Both against
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and
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, the altered reality was incredibly blatant and intruding. When combined with the drastic visual effects of broken techniques, it is incredibly doubtful that nothing would be represented in the apparent Genjutsu battle.
Based on all these points, it should be apparent that the evidence simply doesn't stack up. Not only is the evidence supporting the claim scant at best, there are multitudes of scans, patterns of counters that negate the hypothesis. It is therefore safe to conclude, the Raikage is
not immune to Genjutsu.