Ryudamon is the partner of Masuken Kana, and was originally a Samudramon. However, he was defeated by DexDorugoramon, and reverted to a Digiegg. After temporarily Death-X digivolving into DexDorugamon, he was reborn as Ryudamon, who called Masuken "master". He would later become Hisyaryumon, and later Owryumon.
As they were falling from the air, Masuken knew they needed a digimon who could fly, so he forced his digiegg to digivolve into DexDorugamon. After falling for a trap, however, DexDorugamon reverted to Ryudamon.
When Hikaru believes he has killed Teru, he causes his Dorumon to digivolve to DexDoruGreymon but then realises that the Teru before him is an illusion. Masuken switched the real one to anger Hikaru. He then sends out his digimon, a Samudramon who then fights DexDoruGreymon but is unable to stand up to the power of DexDorugoramon (who Hikaru caused to digivolve).
Hisyaryumon is the partner is of Masuken Kana, and is formerly a Ryudamon. Ryudamon became him while the two were undergoing a test given to them by the Holy Knight, Duke of Courage MedievalGallantmon. They were challenged by a number of prehistoric-themed digimon, including a SkullBaluchimon. Hisyaryumon defeated them. Later, he became an Owryumon.
Masuken was under the control of a MetalPhantomon in Chapter 2 and Hikaru receives a message from Masuken on his Digital Monster D-Cyber Version 1.0 to head North and find him at MetalPhantomon's lair. A battle ensues and Teru tells Hikaru not to argue with Masuken and that he wants to remain in the Digital World, believing Masuken that MetalPhantomon will give them power. Hikaru strikes Teru and tells him to wake up. In doing so, Teru is rendered unconscious. Masuken believes Teru murdered and orders his Digimon to come out, a Samudramon. Hikaru's Digimon Death-X digivolves to a DexDoruGreymon in his grief and guilt. In trying to recover Teru, Hikaru realizes Masuken's trap and that the Teru before him isn't the real one, an illusion. Masuken switched the real one to anger Hikaru. Masuken tells his Samudramon to kill him and send him to the "God of Death", but his Samudramon is defeated by Hikaru's DexDorugoramon.
Masuken's partner is originally a Samudramon, but is defeated by Hikaru's DexDorugoramon. It reverts into a Digi-Egg, and temporarily becomes a DexDorugamon through Death-X Evolution. Finally, it is revived as a Ryudamon. Ryudamon eventually becomes a Hisyaryumon, and after receiving power from the Holy Knights, gains the ability to become Owryumon. Then, finally, Owryumon becomes the blade that allows Alphamon Ouryuken to destroy Dexmon.