ok i like both characters im gonna be fair on this, guy is deffinetly alot faster than itachi, however i believe itachi is smarter, not saying guy is dumb its just itachi is a genius, and for people who say amatersu will burn him then i believe they are rong, guy has the speed to dodge amatersu, again with sword of totsuka, if the sword cant hit then it cant do damage , however getting past susano would deffiently be a problem.
another thing is that it is possible for guy to be put into genjutsu apart from looking into itachis eyes , the moment guy touches itachi there is a possibilty he could be put under genjutsu, however guys speed would deffinetly be another factor here as itachi no matter how skilled he is, might not be able to put guy under genjutsu in time.
guy should deffinetly not be underestimated he is a great force however in this match up i believe itachi has the advantage, but guys 8 inner gates is deffinetly a huge factor in this fight. this is a very close fight IMO and would come down to susano vs 7th gate, however im not sure if guy has the power to break through susano and believe that itachi would win, the only other possibility for guy to win would be if itachi runs out of chakra, which woudnt be much of a problem for guy as he use mainly taijutsu
anyways to summarise i think itachi would win with very high difficulty, but it could go either way
EDIT: great thread

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