Refining
Your story telling skills visually needs polishing. Drama/ beef is clearly there between characters but you need to give these scenes a more stunning presence and impact on the storyline.
There are many techniques to accentuate emotion and action. Shaking your animation when someone is hit, assigning text style consistency between character personalities, showing vulnerbility in your characters in storyline and well cropped cut scenes are a few things that may have enhance your flashes impact upon us.
Flash backs for some background info on Itachi and Kisame could have given us some insight into who these 2 characters are and also generalise the audience for your flash.
There is room for improvement here and surely it will be evident in your next flash.