Looking through that flashback, I can't help but begin to wonder if the original Akabane Sousei was actually just a normal dude who became an actor for the show version of the Dragon Keepers.
Then, during the invasion, maybe he became the first real Red Keeper, but died and the Sousei we know is just one in a line of clones created afterwards and implanted with the original's memories to give the Keepers some form of continued legitimacy.
And the sociopathy comes from the disconnect between the original Sousei's memories and the programming that Ryuujin (probably) implanted to keep him in line. And/or make him believe he is Red Keeper as he appeared in the show.