Tagiru and company are enjoying a day of fishing at the beach when a Digimon Hunter, Mizuki, and her partner, Submarimon, appear. Mizuki, also a treasure hunter, tells them of a sunken treasure in a cave in DigiQuartz that she can't reach because it's guarded by an evil Digimon called Dagomon. She asks Tagiru and the others to Hunt Dagomon for her, so they follow her to the undersea cave, where they find much more than just Dagomon...
(Numbers indicate order of appearance. Bolded characters are fought by the protagonists, and italicized characters appear only as a voice or silhouette.)
Submarimon Type: Aquatic Special Moves Oxygen Homing Submarine Attack
Clockmon: "Submarimon! A Digimon who can swim freely underwater while someone rides on its back!" Old Clock Shop Man: "Its Special Move is firing high-pressure oxygen at its enemies (Oxygen Homing)!" Tagiru Akashi: "DigiXros with ZekeGreymon! DigiXros! Go, super-big ZekeGreymon robot!" Gumdramon: "A robot of justice that beats evil monsters!"