The Return of Kai
It's the continuation of the Justice 5 Tournament with the BEGA Blader’s leading the battle with two wins and a tie. If G Revolutions lose the next battle, they're out and BEGA (led by the evil Boris) takes over the Beyblading Empire. The next battle is set to pit Tyson against Garland, but when the G Revolutions enter the stadium, they reveal their fifth team member- KAI!! Everyone is stunned, except for the BEGA Blader’s who see him only as a loser. Kai is out for revenge because a few days earlier he lost a battle to Brooklyn. So, wanting to save face, Kai calls out Brooklyn, who arrogantly accepts his challenge. A massive battle ensues with Kai trying desperately to somehow attack his opponent, but nothing seems to work. And what's worse, Brooklyn seems to be copying Kai's every move. Kai becomes frustrated and realizes he must dig deep within himself to draw out more power. He does, however, it's making him weaker and weaker. The rest of the G Revolutions team wants him to quit. Kai refuses and in the end, he prepares for a final assault against his foe!
Aired 24/11/2003EP 46 - The Return of Kai

Beyblade G Revolution
After keeping their BitBeasts out of harm's way, a new world championship tournament is announced, but the defending champions can't all be on the same team. Their friendship will be tested and tried as each Bladebreaker goes on a quest to prove why they are the best Beyblader around. Tyson, Max, Ray, Kai, and newcomer Daichi, must keep up their winning ways...even if they must face each other. But, after the tournament is over, what awaits them is an old foe, Boris, taking over the BBA and transforming it into BEGA, the Beyblade Entertainment Global Association. To save Beybladers of the entire world from BEGA's corruption, the Bladebreakers must reunite once again...
(Source: Anime News Network)