An invitation to Banana Island's most celebrated event, "Banana Matsuri," has been extended to Anpanman and his companions by the spirited princess and her humble subordinate Banna. Unfortunately, this paradise is unexpectedly struck by inclement weather and a chilly day destroys the entire Banana crop. To uncover the source of the problem, they investigate Banana Mountain but are confronted by a terrifying aquatic beast that seeks to reclaim the island for the water realm. Can Anpanman and his allies save the island with Banna's assistance in the midst of this disaster?