"A Dangerous Mission! Journey to the Land of Waves!" (重要任務!波の国へ超出発!, Jūyō Ninmu! Nami no Kuni e Chō-shuppatsu!) is episode 6 of the original Naruto anime.
After successfully completing another D-ranked mission, Naruto relentlessly asks the Hokage for a higher level mission. Team 7 is assigned to a mission escorting master bridge-builder Tazuna to the Land of Waves and protecting him while he finishes building his bridge, this task being a more difficult C-rank mission. On their way to the Land of Waves, two chūnin-level ninja from Kirigakure emerge from a puddle and ambush them. The Demon Brothers apparently defeat Kakashi and then turn to the genin and Tazuna. Before the two have a chance to attack Tazuna, Kakashi reappears and effortlessly defeats them. Kakashi is disappointed with the way Naruto poorly handled the situation, then proceeds to compliment Sakura and Sasuke for their courage. Sakura then suggests to quit the mission since Kakashi pointed out that Naruto's wound is poisoned. Naruto, unwilling to jeopardise the mission, takes out a kunai and stabs his hand with it in order to remove the poison. He then makes an oath that he will never run away or back down from any mission, threat, or enemy and that he will not lose to Sasuke. Kakashi observes that Naruto's wound had already begun to heal and assumes that it was due to the healing power of the Nine-Tailed Demon Fox. Subsequently, Gatō, who hired the Demon Brothers to eliminate Tazuna, is shown complaining about their failure and states that there is a high-level ninja accompanying Tazuna. Zabuza, apparently the boss of the Demon Brothers, threatens Gatō with his Kubikiribōchō. He states that he is the Demon of the Hidden Mist and that this time he himself will go and eradicate Tazuna.
According to Hiruzen, the available D-rank missions are: babysitting the chief counsellor's three year old, helping the chief counsellor's wife shopping, and taking up the potatoes.