kakashi it can't be zetsu clone because he was crying when he was trying to kill him.
i never saw Zetsu cry, clones don't have feeling

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rin can't be zetsu clone because he was crying when he was trying to kill him.
its because kakashi was crying.
it proves two things.
1. Kakashi wasn't under a genjutsu because you don't know what you are doing when in a genjutsu.
2. If what kakashi killed is a zetsu clone then what would have happened to the real rin ? also there is no point in developing rin's character.