A Legend from the Hidden Leaf: The Onbaa!

is episode 185 of the original Naruto anime.

Synopsis
A legendary creature, the Onbaa, is the central focus of this episode, attaching to Naruto's back and causing havoc wherever Naruto goes. Despite Naruto's efforts, it remains firmly attached to Naruto's back. Tsunade mentions that Jiraiya once fought the Onbaa, although Tsunade paid him no heed at the time, believing him to be a fool. The Onbaa continues to increase in size, eventually becoming larger than Naruto himself. However, during a mission, it aids Naruto, causing Naruto to reconsider their relationship, but the Onbaa's mother appears, driving Naruto off and claiming her offspring. The child manages to calm the mother, and the two leave. As Naruto returns to the village, most of the inhabitants have Onbaa on their backs, something Naruto takes in with great gusto but does little to remedy.