Naruto: Season 2, Episode 90

2 - 90: Unforgivable! A Total Lack of Respect!

Jiraiya and Naruto catch up to Tsunade, whereupon she learns that Konoha wants her to be the 5th Hokage. She refuses the title, angering Naruto, who mistakes her for being a weakling. Naruto learns first-hand how strong she really is. Naruto decides now is the time to try out the Rasengan, only he hasn't perfected it yet.