Ryo Sakazaki and his buddy Robert Garcia unintentionally stumble upon the lair of a jewel thief while trying to save a feline. The pair witnesses the gang of bandits executing the thief and narrowly escape a scuffle. While attempting to flee, they discover that the thugs are in cahoots with Mr. Big, a notorious kingpin in South Town. Their troubles escalate when they learn that Mr. Big suspects them of pilfering the prized "Eye of Sirius" diamond and that he has taken Ryo's sister, Yuri, as ransom. With few alternatives and lacking the diamond, Ryo and Robert must battle their way through Mr. Big's fleet to free Yuri before it's too late.