Ge Kai had been disgraced after the last attempt at the retrieval of the Purple Sapphire that he had led to the house of Zhang Jian on Mount Dabie. As a result the loss had been so severe that Ge Kai had lost all its authority and position that it had built up through his achievements and the acknowledgement of Zero.
Ge Kai had been left to fend for himself after he was stripped of the Dragon Sword that he had snatched with his own abilities in order to prove himself to Zero. Since his faction had fallen, it couldn't have gone against the Demon leader and as such couldn't escape the fate of being discarded.
After that Ge Kai had vowed to himself that he had to get stronger on his own. He had to lay low for a while until no one was wary of him, gather and develop his strength and repay the disgrace that had been thrust on to him by a hundred times.