Dorumon became a Grademon after losing his Dragon Spirit. He is first seen as a Dorimon when Hikaru reachs the Digital World. He first evolves to Dorugoramon when he battles Teru's MetalGreymon X. He later digivolves to DexDoruGreymon and DexDorugoramon in order to fight Masuken's Samudramon. After he loses his Dragon Spirit, he met Omega of the Royal Knights, who told him that he must pass some trials in order to get another Dragon Spirit from Duke of Courage. After he passed the trials and defeated Duke, he receives his Dragon Spirit. In order to defeat Dexmon (who MetalPhantomon revives to take over the Digital World), he trains with Omega and digivolves into Grademon,Alphamon and finally Alphamon Ouryuken. He defeated MetalPhantomon and then his creation Dexmon and saved the Digital World.
He is the Digimon partner of Hikaru Ryuuji and he acts like Hikaru's little brother. At first he doesn't agree with Hikaru's actions, but through their adventures they became close friends. He first digivolved to Dorugoramon the next day of Hikaru's arrival in the Digital Word in order to protect his partner. It is revealed in the ending that he was Alphamon the lost leader of the Royal Knights.
DoruGreymon is the intial ultimate form of Dorumon.
Dorugoramon is Dorumon's intial Mega form.
When Masuken makes it look like Hikaru killed Teru, Dorumon digivolves into DexDorugoramon. This attracted the attention of Omnimon X, who proceeded to fight DexDorugoramon. After Hikaru threatened to stop being friends, he calmed down.
Alphamon is the final form of Dorumon. In the manhua's final battle against the ancient Dexmon, he's revealed to actually be Alphamon, the leader of the group known as the Holy Knights, from long ago. Alphamon and Owryumon DNA Digivolve together to form Alphamon Ouryuken.
Alphamon Ouryuken appears when the powers of Magna, one of the Holy Knights allows Owryumon to become a sword for Alphamon. Alphamon's appearance changes, with feathered wings on his back and Owryumon becoming his sword, the War Blade.