The New Erotic Ninjutsu Completed!!

is a manga-omake included with the second Naruto fanbook.

Summary
This omake is set during the two-and-a-half years that Naruto spends training with Jiraiya between Part I and Part II. After a day of training, Naruto is eager to cook a fish that they caught. Jiraiya, meanwhile, has writer's block for his next Icha Icha novel, and is unwilling to cook Naruto's fish. Naruto uses a New Sexy Technique to convince Jiraiya, and Jiraiya happily complies. As Naruto celebrates, Jiraiya decides to use Naruto's Sexy Technique as inspiration. He suggests Naruto wear a thong as part of his transformation. Confusing a thong for a mawashi, Naruto transforms into a sumo wrestler. When Jiraiya becomes angry with him, he uses the form to knock Jiraiya out.

Trivia

 * This omake marks the only time Jiraiya has ever used the Fire Release: Dragon Fire Technique.