Giliath Osborne saved his son Rean Schwarzer by having his own heart transferred to his son. His heart, however, was under influence of Erebonia's curse. As a result, the young Rean obtained a dangerous power referred to as ogre power. He gradually learns to gain control over that power. The power becomes uncontrollable when Rean sees his friend Millium Orion sacrifice herself. At that point, Rean is branded as the Sacrifice.
The reason Rean Schwarzer was chosen as sacrifice by the curse was in order to have a spare of Giliath Osborne, who served as the curse's main body. His ogre power and subsequently white hair and red eyes serve as a mark of his destiny as sacrifice.