=======================================
Near the dawn of the Eternal Empire the Tora Clan of the Oni was swept into a feud with the mortals. Summoned and Bound by the Empire's enemies, the Oni were used as shock troops against the forces of the Empire.
Both sides suffered terribly. This was to be expected. The Oni are masters of destruction. However, they did not expect their might to be matched by the weak mortals. These humans eventually earned the respect of their Oni enemies. On the brink of the Tora's defeat and likely eradication, the Emperor himself brokered a peace between the Tora and the Empire. The Emperor broke the Tora's Binding, freeing them and allowing them to turn against the diabolists that had forced them to serve. The remaining members of the clan were spared so that they could return home, and one member of the Tora clan remained as the protector of the throne and the line of the emperor.
That was the price of defeat. The Onitora would send one warrior to serve the Eternal Empire itself, and during times when the Emperor did not sit on the throne, the chosen Mamoru would seek the True Emperor's ascension.
And so, since that time, there has been an Onitora bodyguard standing behind the throne. The Tora do not like this ancient debt, but the powerful curses and geas that would incur if they were to break their vows ensure their cooperation. Besides that, the Tora are among the most honorable of the Oni, and would sooner die than besmirch the honor of their clan or themselves.
The last Mamoru has fallen and the ancestral blades returned. A new Mamoru has been chosen, or perhaps cursed, by the powers of the ancient pact. The duty and the blades have passed to a new bearer. He is barely more than a youth, still growing into his might and full of zeal.
He will find his charge and fulfill his duty. Woe be it to anyone in his way.