Nintama Rantaro the Movie: Ninjutsu Academy - All Hands on Deck!

Sinopsis Film

The Ninjutsu Academy students return from summer break to hear that due to one of Komatsuda's mistakes, all their summer homework was mixed up. As a result Kisanta, who received an assignment meant for a sixth year, has gone missing after trying to sneak into Oomagatoki Castle to steal their lord's fundoshi. A group including Shinbei and Kirimaru is sent to rescue him, but since Oomagatoki is at war with Tasogaredoki Castle it might be a difficult mission.