Later he wished he'd never seen that sketch. The one hanging over the costume in Ethan's shop, it all would have been better, simpler, if he never dressed up as that man. At the time he had not known anything about that manga/anime and if he'd known what the man stood for, he would have not even touched, not even thought about dressing up like that.
But at the time all he saw was a sketch of a stoic looking man in a black tunic of sorts, with clawed gloves and incredibly long black hair.
He'd been drawn to that sketch, to that costume. Ethan had given him the costume for almost free and he'd been so happy... until the spell changed them into their costumes.
And Xander Harris became Touda, the Leaping Serpent, one of the 12 highest ranked Shikigamis and ruler of the black flames from Hell.
For one moment the shikai no hakaisha stood there not knowing what had happened, but then all hell broke loose.
If not for the interference of the Powers that Be, the world would have stopped existing that night. But their interference was not without a price to be paid. While the others were returned to their normal state of being, his two minds were merged into one.
Shikigami he had become, Shikigami he would remain... for the rest of his eternity.
They send him away, to a newly forming dimension. To give him a second chance, they said, but he knew better. He'd been too strong and too dark to remain in his home dimension.
And so he went and watched as a new dimension came into being. He saw the forming of the different worlds from a handful of dust. And there, in the Gensoukai he found others like him, other Shikigamis. Sohryuu, the Waterdragon, Suzaku, the Phoenix, Byakko, the Windtiger, Genbu, the Turtle of the earth and many others, but they all remained distant to him, for they were afraid of his powers. The power of Hellfire, that could even kill a Shikigami.
So time went by and he amused himself by working for the Golden Emperor... but even that went boring after several eons. One last order he would fullfil, he promised, but than he would ask for his release. The Golden Emperor gave him that order, but when he returned, to be released from his position, he was arrested and tied as a traitor. The Golden Emperor had decided that his powers were too dangerous and had set him up.
He didn't defended himself at his trial, why should he? Who would believe him, anyway? Once again he was called shikai no hakaisha and sentenced to life in darkness. They chained him up in the deepest, darkest cell of Tenkuu and left him there.
In the darkness days bleed into each other as time became meaningless, weeks bcame months became years became decades.
But then, one day, a bit light entered his prison, in form of a young Shinigami with violet eyes, who broke his chains and offered him his hand.
For a moment he looked at the hand bewildered. In all his time as a Shikigami, nobody ever had offered him his hand. He looked up, straight into the eyes of the young Shinigami and made his decision. For in the eyes of the young man, he could recognise innocence and trust like he hadn't seen since the oh so very far away days when he had been Xander. His own innocence had died away and his trust had been terribly shattered, but he wanted to protect the young one, for he still had so much of it, despite his dark and often bloody job. There would be sacrifices to be made, he knew that, and the other Shikigami would avoid and hate him even more than before, but, and he watched the innocent eyes light up, it was worth it and he took Tsuzuki's hand.
Shikigami: Spirit God
shikai no hakaisha: Destroyer of worlds
Gensou Kai: Spiritworld
Tenkuu: a living building and strong Shikigami in itself
Shinigami: Angel of Death