Slicing your argument to ribbons
A decent counter yet lacking in many respects. Kisame would more than capable of dodging Sasori's attacks as shown when he was capable of keeping up with Gai even with a few of the gates unlocked. His basic speed would be more than enough to avoid Hiruko's trap mechanisms especially with the stated range of the fight. Being in Akatsuki, it seems each of the members possessed a fundamental level of knowledge on one another. This is shown to be true when
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, implying he knew of their immortality and what it entailed. The same could be said about Kisame having knowledge of Sasori's poisoned-drenched weaponry, causing him to remain cautious throughout the whole fight and evade every attack by whatever means. Another tactic he could possibly employ is using clones to fight his opponent in close-range whilst he provides long-range support to prevent risking being scratched by even one of Sasori's attacks. Their ability to liqeufy and survive against any physical attacks would allow them to easily close the gap and come within short range of the puppeteer, exposing his severe weakness. Once in close-range, Kisame's clones could re-use a tactic utilized by Kisame against Team Gai, which involves trapping Sasori in an extremely dense prison of water. The prison of water would prevent even the slightest of movements, stopping Sasori controlling Sandaime Kazekage through moving his fingers. Once trapped and defensless, Kisame could land a fatal hit through various means
Furthermore, dodging the attack via movement isn't Kisame's only option in dealing with Sasori. Unlike Kisame, Sakura and Chiyo had no elemental affinities or tools to block Sasori's attacks except using her puppets. Whilst her puppets were a suggestible defense for avoiding Hiruko's traps, its use was negated once he unveiled his 3rd Kazekage Puppet and hence Iron Sand. The Iron Sand was shown to be capable of
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, preventing any maneuverability and therefore relinquishing its defensive use to Chiyo as the puppet could no longer move to intercept successive attacks. Unfortunately for Sasori, Kisame is capable of manipulating Water Release on a scale like no other. In response to Hiruko's attacks, he could spew a stream of water, create water sharks or utilize other constructs of water to clash with them, wash off the poison and knock them off their original trajectory and therefore keeping Kisame unscathed.
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In dealing with Iron Sand, Kisame could simply take advantage of its various weaknesses. On numerous occasions its been shown that
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and come together compared to Gaara's sand, making it much slower in preparation for an attack. This becomes even more apparent through Sasori's usage of Iron Sand as he
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rather than fluid manipulation similar to Gaara and the Fourth Kazekage. Despite the Fourth Kazekage manipulating his gold dust through the same means as Sasori, it leads me to believe as a puppet that Sandaime Kazekage is physically incapable of fluid manipulation of his Iron Sand due to the nature of puppetry. As a direct result of this, Sasori cannot in fact use Iron Sand as a means of aerial elevation, he can't form waves, shields and domes of Iron Sand to fight on par with the scale of Kisame's Suiton and his manipulation of the 3rd Kazekage's Sand is obviously limited by the nature of puppetry, meaning his usage of the the potentially dangerous tool is greatly hampered. You can use doubtful claims such as Iron Sand breaking the sound barrier and such, but all of that is negated against the fact the attack requires much preparation time in compensation. In the time Sasori prepares bullets of Iron Sand, Kisame could easily have created an immense wave of sand which dwarfs his opponent's attack entirely. Regardless of what Iron Sand offensive is thrown Kisame's way, the time of coagulation is enough for him to launch his own suiton-based attack, thus deflecting any and all of Sasori's attacks.
Thus far I've established nothing in Sasori's arsenal is "undodgeable" and so possess no threat to Kisame. To further reinforce my argument I'll quote a good friend of mine
It hasn't been shown canonically for Sasori to manipulate Iron Sand in such a way and therefore is a terrible argument to employ. With that, Sasori literally possess no counter for Kisame's large scale suiton attacks and is pretty much a sitting duck waiting to be devoured by a menacing shark.
Beyond the Fourth Wall
Once Hiruko reaches the peak of its effectiveness (either through being broken or relinquished by Sasori himself), Sasori would now possess the common weakness of puppeteers his Hiruko puppet sought to destroy. He would be vulnerable in close range and unable to fight his opponent. Kisame's fighting style naturally includes closing the gap between himself and his opponent and engaging them in close quarters. Once he does this through the various means available to him (clone feints, movement, a ride-able wave of water), Sasori would become more than powerless against his foe.
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would inevitably result in the chakra strings connecting himself and the 3rd Kazekage to vanish, stopping further manipulation of his puppet and leaving him almost powerless to act. With no time to re-attach his chakra strings and launch an attack, its more than likely he would resort to using himself. However, in such close-range the situation wouldn't change significantly. His deployable flamethrowers would be absorbed by Samehada and converted into Kisame's own stamina, his poison rigged-tools wouldn't act fast enough to intercept Kisame's kenjutsu offensives and his puppet body would prove to be useless in Taijutsu. One glaring disadvantage of unveiling himself to be a human puppet would display his core, his center of chakra and the only living part of him which remains. Such a concentrated quantity of chakra would more than offset Samehada and alert Kisame to such a weakness. As a result, his future attacks would be centered around the area containing his core, each swing whether it connects, is blocked or narrowly misses will gradually sap chakra out of a defenseless Sasori.
Blown out of the water
The quote utilized by me was obviously written for a specific purpose. In that thread I was supporting the underdog and so constructing whatever argument available to me. The reality is, very few people can effectively counter the water dome once its fully constructed. You speak of the poison seeping into the water in the vicinity around Sasori yet focus little on my point concerning it diluting into the vast expanse of the structure.
I'm sure you're familiar with the concept of dilution which initiates the process of making a chemical weaker or less concentrated. Now look at the construction of the water dome,
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. This is exactly when all of Sasori's poison-drenched tools will become cleansed of harmful chemicals. With the poison-drenched weapons being cleaned before Kisame's in the area of effect, the principle of dilution will dictate that it will eventually evenly distribute itself along the massive entirety of the dome, weakening into the extent it becomes negligible in potency.
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