The story centers around the life of a young boxer named Ryuuji Takane and his sister Kiku, who is also his coach. Their father had been a famous boxer but is now deceased. Ryuuji and his sister both inherited their father's talent for boxing: Ryuuji inherited his strength and techniques, while Kiku picked up his talent for analysis and strategy. Ryuuji and Kiku leave home to train and become famous in order to help their lonely mother. On the way to stardom, they have to defeat the strongest challengers all over the world.