Melonpanna and Rollpanna, who were once separated, make friends with a enigmatic horse named Marin. Marin reveals to Rollpanna her prized possession, an underwater vessel she salvaged from the depths. Baikinman becomes aware of this and is motivated to create a phantom ship with Dr. Hiyari's assistance. He also schemes to corrupt Rollpanna entirely, intending to use her to eliminate Anpanman.