I will debunk the argument of those who think Itachi has a chance against Killer Bee-sama.
Nature Transformation of Uchiha Itachi
As Uchiha, Itachi is naturally gifted with Fire nature and he also has Water nature as extra. With his Fire chakra, he can create ball of fire [
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] and Shuriken mixed with it [
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].
Bee can counter this arsenal with either the use of Samehada's ability to absorb chakra [
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] or the use of Hachibi's cloak by tanking it with no damage as displayed by Naruto.
Itachi's Ocular Powers
Tsukuyomi
Itachi's most powerful Genjutsu allowing him to manipulate time and control spaces. However, using it will be pointless against a perfect Jinchuuriki:
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Thus Tsukuyomi rendered useless.
Amatersu
Itachi's most powerful attack. Black flames which were hyped to be hot as the sun. But according to the manga, Killer Bee already has info on the respective Jutsu thanks Uzumaki Naruto:
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As we know, Itachi's needs to charge a large amount of chakra so he needs to close his eyes. Bee will notice it and use his Shunshin no jutsu to confuse Itachi making it harder for him to KO. Similar tactic to Sasuke's running away from Amatersu but Bee is using his full speed this time. In case he gets hit, he can transform into V2 and push them away.
If you notice when Jinchuuriki transforms into V2, a high amount of density comes out of them such as this:
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Which is very similar to Nagato repelling Amatersu via Shinra Tensie:
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By this, Shinra Tensie is repelled from Bee and he can use Hachibi's chakra to heal his wounds.
Susanoo
With Itachi beat up to no end, and decides to manifest Susanoo. He will access to Yata and Totsuka, however Bee's firepower is too immense for Itachi to handle. He can simply keep running forcing Itachi to die of exhaustion or charge with a TBB and finishes him.
Manga knowledge, bee knows about amaterasu and doesn't mess around while in full bijuu mode. When he transforms, he immediately goes rapidfire bijuudama and blocks amaterasu with a tentacle or limb, then henges out of it like what he did against sasuke. He doesn't get close enough for itachi to totsuka him, and can use his whirlwind in order to create distance if needed.
If bee messes around or had no knowledge, he'd probably lose which is basically how everyone who fights itachi loses to him.
Actually Itachi would win this high diff but your condition says Manga Knowledge, in other words KB knows about Amaterasu, Tsukuyomi, Susanoo, Yata, Totsuka, Izanami etc So he takes this one high diff U_U