Hunter x Hunter - episode 6 - 19 Nov, 1999

Gon, Kurapika, and Leorio reach the first stage of the Hunter Exam, a seemingly endless forced run through a tunnel leading by the examiner named Satotz. They are befriended by Tonpa, a man taking the exam for the 35th time, and meet Killua, another entrant. In the end Tonpa betrays Leorio, as Gon and Kurapika go looking for them. (Source: Wikipedia) Hunter Exam arc: (6/31)