The Great Undersea Adventure! Find the Treasure Digimon of Dreams!

While out fishing, Xros Heart meets a female Digimon Hunter Mizuki and her partner Submarimon. Explaining her story, Mizuki is treasure hunter who heard of a treasure within sunken ship under Tokyo's waters. However, to defend the beautiful sea, and to obtain riches, she became a Digimon Hunter to deal with Dragomon (who is also pursuing a Plesiomon). Asking for Tagiru's help, Mizuki leads Xros Heart to Dragomon's location as he is also searching for something valuable. Tagiru helps to capture Dragomon while Mizuki manages to capture Plesiomon.