"Who are You?!" (お前は誰だ!!, Omae wa Dare da!!) is chapter 16 of the original Naruto manga.
Kakashi checks Zabuza's pulse and, not being able to find one, concludes that the masked boy has killed him. Suspecting that the boy is a Kirigakurehunter-nin, Kakashi allows him to do as he wishes, telling Team 7 that it is the job of hunter-nin to track down and eliminate missing-nin like Zabuza. Naruto is angry that someone so young could kill someone as dangerous as Zabuza, but Kakashi informs him that it is something he will need to get used to. The boy leaves with Zabuza's body and Kakashi promptly collapses, having been left exhausted from overuse of his Sharingan. He is taken to Tazuna's home to rest. Meanwhile, the boy revives Zabuza, having only pretended to kill him to save him from Kakashi.