If you mean the one where you help Gai do Kakashi's mission then you gotta do 3 additional hits. You can just start the hits and let him finish them so you don't kill him easily. I use Itachi and use his ground throw and hit Up+O right away so it starts the additional blows. But that's just my strategy.
i think there is another forum asking the same thing and i already answered on there so check that out
its called does anyone know how to do 3 substitution hits
its easy to beat this game
funny thing that there is a code to unlock almost all the character but since this was my first ultimate ninja game I wanted to play it by the book