Notes:
Danny Phantom:White Knight (Yes he still has his hazmat suit on under there)
Black Knight: Ghost King (with slightly different armor) (Yes, Pariah has been injured before, if you remember his episode in the show, you know he has scars, a broken horn, and an eye patch, and his skin is white with a green eye. Just imagine that he seemed to get even paler.) (The reason I am not correcting these errors in the text because I wanted to show you the original, unaltered document as Sage of Eyes gave me when he gave me permission to use the story.)
Basically, Pariah Dark got out of the Sarcophagus of Forever Sleep, and unleashed the most terrible war in history, causing the deaths of most of humanity and pretty much every ghost in the Ghost Zone, save Pariah himself. Danny then fought against him, trying to keep him from using the souls of the fallen that obviously ended up in the Ghost Zone to gain more power, and the energies unleashed warped the ghost zone, turning it into Hueco Mundo, and transmuting most ectoplasm in the main realm of the Ghost Zone into spiritual matter, and sealing off the smaller pocket realms behind the door portals (Yes, Danny still has all his ghost powers). When Danny awoke from the aftermath, he had lost his memories, and created his own realm, which is called the White realm, as he unconsciously gathers so much reiatsu that it creates a mist that can dissolve any spiritual matter on contact.
Also, if anyone wanted to know, the name of the White Knight's sword is Sourukira. Translated, (as souru means soul and kira can mean killer) the name is literally "soul killer".