Minato dont even need to be in the dome. He would just FTG out and wait for Kisame. Brains over brawns, no idiot is going to stay in there to just swim around with someone who is made to swim. He might as well transport the dome into a lava and call it a day if Kisame dont want to come out.
Even His clone can do this, the original don't even need to be there. Its already proven that his clone can do Harashin. Better than worst Minato is a genius, he can use his clone as bait so Kisame can go touch him to steal chakra and just tag him while he at it. Once Kisame is tagged it is over, Minato can teleport to him anytime, or teleport Kisame out anytime. There's a lot of factor, plus if you talking about KCM, that means he have access to Kurama powers, which in this case his rasengan power scale should be around a Bijuu bomb level, easily destroy that water dome.
Even His clone can do this, the original don't even need to be there. Its already proven that his clone can do Harashin. Better than worst Minato is a genius, he can use his clone as bait so Kisame can go touch him to steal chakra and just tag him while he at it. Once Kisame is tagged it is over, Minato can teleport to him anytime, or teleport Kisame out anytime. There's a lot of factor, plus if you talking about KCM, that means he have access to Kurama powers, which in this case his rasengan power scale should be around a Bijuu bomb level, easily destroy that water dome.
The bolded are entirely wrong, sometimes baseless.
Let's start with this. Minato's speed is not even capable of being compared to Kisame's or Bee's when underwater. Bee has been shown using the extra tails as a way to propell himself through the Water Dome. Whereas Kisame has proven that both when and when not transformed, he is a speedy bastard in water.
Minato will be swimming, yes. Swimming. Not running. Who's to say he can even swim as fast as he runs? Look what happens here to Bee, a fast shinobi when he is forced to swim[You must be registered for see links][You must be registered for see links]. Yes, caught in seconds. In the Water Dome, foot speed is not a factor.
Now, from here we can counter the shadow clone plot you have hatched for Minato. While, it is a good idea. Kisame won't be falling for it. You've mentioned the fact that KCM gives him near limitless chakra, apparently? Look how quickly the Hachibi's chakra was absorbed here[You must be registered for see links]. KCM won't be lasting much longer then that.
Returning to the Shadow Clone Argument, nah. Kisamehada is a sensor[You must be registered for see links]. I am fairly sure that he would be capable of pointing out which Minato is the real one. As for the reverse summoning. Who's to say that Kisame himself does not use the Five Feeding Sharks Jutsu to trail on SWIMMING Minato and catch him in that. And, if you have thoughts about Minato escape. Think again.
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Anything caught in the current will not be capable of escaping without being ripped apart. Quite the deadly jutsu, no? And, if this counter does you no good. Who's to say Kisame does not form a Mizu Bunshin or two before putting this Water Dome up? With each Mizu Bunshin, they could technically be capable of fusing with Samehada and gaining the same abilities as the original.
Just a few points that I should have mentioned earlier, that you may think are incorrect. I'll take this time to clear up my last two paragraphs. The Five Feeding Sharks is indeed a ninjutsu capable of being used by Kisame. It requires simply a dash of blood and a thrust. [You must be registered for see links] [You must be registered for see links].
And, as for the Mizu Bunshin idea. It's not entirely out there to think such a thing. The Mizu Bunshin have ALL capabilities as the original, just to a lesser extent. The idea of them possessing a fusion form; Something that hasn't even been shown to rely on chakra, and even if it did would be no problem for the clones of Kisame. Is an entirely plausible thing.
If you still do not believe me on the Mizu Bunshin idea, take a look at what the DB has to say on this jutsu.
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So, Kisame could either trap one of the Minato's, once again. Swimming, not foot speed. There is nothing to suggest he is capable of rivaling Kisame or Bee in the water, and he has yet to reveal chakra arms to help push him and increase his speed. Or, he could have Mizu Bunshin, before the Water Dome arises, to track down and capture and drain one of the Minato's.
This might get to the part where you assume that he can't have this sort of prep, the OP has stated no such thing and without knowledge; I doubt Minato would notice the Water Dome Moving swiftly enough to explore the idea of leaving a kunai behind to get washed away. So, I shall assume it's full knowledge.
An added note; to all who are using the Naruto blitzing of Kisame; Stop it. He was incredibly weakened at that point. His movements were lessened, it's obvious at how much of a disadvantage he was. While I am not saying Kisame can react to everything. There's no need to assume that every simple thing that any speedy character does to him will catch him of guard and defeat him.