On Lion-O's 20th birthday, he must pass a set of trials to become the true Lord of the Thundercats. Even though he is the hereditary Lord of the Thundercats, he has not proven himself to be worthy of that title. Lion-O must prove that he is he lord of the Thundercats by facing his friends and fellow Thundercats alone and unarmed.
His first test is to beat Panthro in a duel to test his strength.