Kai Syaoran had tried to fix the Frenzied Dragon using the power of the Dawn Soul gem, and he had managed to repair all the damage that the dragon's soul had suffered. He had not stopped there—he went a step further and purified the soul, allowing it to reach a new realm of being.
Even after all this, the Frenzied Dragon Emperor had still remained unconscious. The soul was a very mysterious thing, and even with all his understanding of this aspect of existence, Kai Syaoran still needed to learn more before he could awaken the dragon.
As the Failed Prince, Kai Syaoran delved deeper into the soul and the realm of consciousness. After millions of years, he had become a master in matters of the soul. He created a Rune that would pull the Frenzied Dragon Emperor out of his consciousness, where he had instinctively hidden himself when his soul was damaged.