Carlos Rivera is a Venezuelan bantamweight boxer who ranked #6 in the world. The reason he is called a "A King Without A Crown" is because there is a rumor that the world champion is too afraid to fight him. Yoko Shiraki brings Rivera over to Japan to help Joe recover.

Spoiler

After his 12-Round Match with Joe, Carlos goes to Mexico City to fight the Champion Jose Mendoza, but is knocked out in the first round, 1 minute and 33 seconds in. After the match, his manager, Robert, claims, “Carlos Rivera did not lose against the champion, Jose Mendoza. He was already broken by an unknown Japanese boxer named Joe Yabuki” confirming that Carlos was left punch drunk after his match with Joe. While offered a rematch with Jose, Robert turns it down and says that Carlos may never step into the ring ever again