Sensei and Student: The Bond of the Shinobi

is episode 100 of the original Naruto anime.

Synopsis
Guy and Lee discuss the operation, and Lee expresses his fears of dying as well as his fears of never being a ninja. The two reminisce about their time together, and Guy finally decides that if Lee dies during the operation, so will he, as he too can't live if Lee isn't a ninja. Guy's words inspire Lee, and he decides to take the operation. Tsunade, meanwhile, manages to increase the odds of Lee's survival to 58%, and is satisfied that Lee will most likely survive the operation. Tsunade is inaugurated as Hokage, and the role as the village's protector is passed on to her.