Let's say for whatever reason the showdown everyone wanted to see was going to happen...
Pain VS Itachi!!
6 vs 1 isn't very good odds no matter which way you put it.
What if Itachi sought the aid of his partner Kisame.
Where would Kisame's loyalties lie?!
Would he help Itachi, his respected partner??
Or would his loyalties still lie with Akatski?
What are your thoughts?!
I doubt Kisame would side with Itachi against Pein, Kisame been with Akatsuki a bit longer than he been partnered up with Itachi I think and Kisame and Itachi might have had some sort of respect but they didn't trust each other. Kisame out right threatened Itachi when they first teamed up and told him never to drop his guard around him and we see Itachi always rocking the Sharingan on so I think even among the years there was a threat of backstabbing. Kisame killed himself so they wouldn't get intel on Akatsuki so I don't think he would betray them. Nagato would also have the other Akatsuki members if Kisame comes into this
Also what could Kisame really do? Deva path pulls Samehada from Kisame and then push it miles away. Pull Kisame and have weapon path laser blast him then pull out his soul for good measures. That would let Itachi see what 2 of the Peins could do but he wouldn't know about the 5 sec interval from that. Summoning path sends the rhino, dog, and centiped with Deva path and absorbing path after Itachi while weapon path flies high above to fire missiles and lasers. Amaterasu requires Otachi to close his eye and look at his target but trying to dodge the missiles and lasers from
Weapon path plus the exploding eggs from the bird would make that really hard. Deva can even pull Itachi to a spot where weapon path is aiming due to shared vision.
Susanoo would buy him some time of protection but what if Deva path pulls Yata and Totsuka blade from Susanoo? This is the guy who was weakened from almighty push who sent 3 giant toads who are roughly Final Susanoo size, miles away from himself causing them to break their bones. Doing that to Susanoo wouldn't be hard for him.