The Assassin of the Mist!

The mist rolls in with a body inside it. Zabuza Momochi, former member of the Mist's Seven Swordsmen, announces himself by parking a six-foot cleaver in a tree and radiating killing intent thick enough to make Sasuke consider suicide just to end the fear. Kakashi answers by lifting his headband: the Sharingan, named and shown for the first time. The ensuing duel on the water — silent killing technique against copied jutsu — is the series' first jonin-versus-jonin fight, and the genin can only watch.