The first time they fought, Guy was focusing on staring at his opponent's legs to avoid staring at Itachi's sharingan.
The second time it wasn't really Kisame but somebody who had shape shifted into him, and from the very beginning Guy knew there was something off about him. Despite that, he did say he seemed familiar or at least implied he remebered samehada. I guess his confusion plus the tiredness from using the gate might've made the next fight confusing to him.
The third time Kisame implied he didn't remember him but Guy never did confirm it and in fact said his full name by the end of the fight. If he really didn't remember him it might be because whenever he saw him there were factors that confused him:
All of this factors combined with Guy's low attention span might excuse his having a hard time remembering the guy.
Log in in order to Post. LOGIN | Register