Nintama Rantarou: Dokutake Onsen no Dan  

忍たま乱太郎 ドクタケ温泉の段

The lord of maitake castle invites the ninjutsu academy headmaster to join him on an incognito visit to a dango shop with rantarou, kirimaru, and shinbei tagging along. however, they soon discover that the shop is actually a trap set by dokutake castle, and it's not just them who have been caught.