Following Ryuuji Takane's victory in the Champion Carnival, the arrival of Black Shaft, the U.S. Junior Champion, sets the stage for a showdown before the impending World Tournament. Alongside Takeshi Kawai, Kazuki Shinatora, Ishimatsu Katori, and Superstar Jun Kenzaki, Ryuuji must demonstrate their boxing prowess not just to Black Shaft but to the global audience. However, Shaft's challenge takes a dark turn as he recruits unconventional contenders: a condemned criminal from Death Row, the leader of the notorious Great Angels gang, a mysterious woman, and the enigmatic 'Dark Emperor of the South.' Amidst these unorthodox opponents, Shaft also engages in negotiations with Don Giuliano, the Italian Junior Champion, adding further intrigue to the evolving boxing saga.