Hunter x Hunter - episode 37 - 18 Aug, 2000

Gon and Killua decide to fight professionally in order to train and make money. They go to the 251-story Heavens Arena, where every 10 floor increase represents more difficult opponents. Gon's power has increased dramatically from training on Zoldyck grounds, and he sends his opponent flying. Killua faces Zushi, another child who is competing, and Killua senses he can use a technique similar to Illumi's. Killua vows to meet Zushi on the top floor to learn more. (Source: Wikipedia) Heavens Arena arc: (1/8)