Itachi wins.
1) I am skeptical Mu's invisibility can work on the Sharingan. I'm skeptical because he and Onoki tag teamed Madara (who was not trying), and got their asses handed to them. If Mu could hide from the Sharingan how did he lose? We've also seen one other invisibility tech just like this one, and the sharingan saw through it.
2) Mu doesn't start the fight inivisible, and Itachi is faster than him and has techs that can one shot him (and do not require seals), so Mu is probably dead before he can do anything. Not to mention Itachi can predict his movements with the sharingan, and invisibility is by no means instant (the body seems to gradually fade away)
3) Being invisible didn't stop Onoki from fighting Mu to a standstill, so assumedly Mu creates an opening when he uses the Jinton (which isn't invisible). This is bad for Mu because Itachi has a shield that can block Jinton, and Itachi is not only portrayed as a genius at predicting what people will do (to the point of being clairvoyant, seeing blind spots, predicting what people will do, where they will attack, etc), but because he has great reaction time and is faster than Mu... he'll also be on the look out for a Jinton forming, and has crows and illusory doubles he can use to further remove space to sneak up on him (and to fake out Mu). So even if Mu starts invisible, it doesn't matter so much, because Itachi has a hard counter to Jinton, and Jinton isn't instant.
4) Even wildly swinging the Totsuka blade wildly and keeping Susanoo on will keep Mu out of close range, and give Itachi even more room to use the Mirror (does Mu even know what the Totsuka blade does? He might try to block it and get sealed), and more room for Jinton to be noticed.
All in all, the fight is probably over in the first moment, when Itachi looks at Mu (and hits him with one of his one shot moves, and/or uses Shi Sui's eye). Izanami doesn't require eye contact either, not that it'll come to that.
Example of opening seconds:
- Itachi uses Ameratsu. Mu is starting to go invisible, but is now on fire and dies (plus loses invisibility)
- Itachi uses Genjutsu (Mu doesn't know how this works remember with no advanced knowledge) Mu starts to go invisib... fight over
- Itachi charges him forming Susanoo as he does. Mu starts to go invisible and mov... Totsuka blade into chest. Sealed.
- Itachi pulls a crow out of his vest, looks it in the eye for a moment before turning it to face Mu who is in the process of vanishing and dodging... suddenly Mu decides Itachi is his best buddy and goes visible and bows before him. Koto'd (given he can impart 72 hours of info in a second, he's going to be able to program it in that time no probs).
