it uses the opponent's chakra and if he tries to attack guy, guy isn't retarded he would use the afternoon tiger on him instead of on the water dome to break out it is a huge shark anyone would notice that, and that would beat his shark missile and give such big shockwave that it will break waterdome.
look at the shock wave
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it is huge, guy would obviously notice if kisame is gonna attack him why would he take his eyes off the enemy he can use the afternoon tiger anywhere in the dome and get out and kisame would lose becos he would be in the blast.