As the only survivor in the Fire that devastated Fuyuki in his childhood, the fire had not only burned him physically, but wore at him mentally. Joy, anger, loss, every emotion within him had been burnt away until there was nothing left. It was to the point that when Kiritsugu had found him, he had grown jealous of the way Kiritsugu could smile so broadly and made it his goal to purse that same kind of happiness. Taking the ideals of another to fill the emptiness of his own existence.