The challenger has become the champion as Ippo Makunouchi now wears the featherweight championship belt of Japan. Some time has passed since Ippo's victory, and he has found his friends and coach as supportive as ever; his crush, Kumi Mashiba, seems to enjoy spending time with him as well. Things are looking bright for the new champion, but just as he once set his sights on becoming the best, his first challenger poses an intimidating threat. Kazuki Sanada works as a doctor at the same hospital as Kumi and fights strategically. Known for integrating his knowledge of the human body into his fights, Sanada is a fearsome contender—however, more unnerving than his physical ability, he has garnered the support of the nurses. Despite being the champion, Ippo feels the pressure as he must face the daunting challenge, retain his belt, and win over the girl he loves. After intense battles, defeating Sendo, Makunouchi Ippo finally grasped the place as the Japanese Feather-Weight Champion. And so, Ippo changes from a "Challenger" to a "Champion", and the opponent of his first defence match is decided. The name of the challenger was Sanada Ikki. A fierce opponent who, aiming for a Dual Class Conquest, returned the title of Junior- Feather Class.Sanada has a different face as a Current Medical University Student, which enables the intimate understanding of the human body, of where a punch should land to deprive stamina and to down the opponent with consistent damage. Furthermore, he coolly analyses his condition from a medical perspective, based on his amount of perspiration, breathing rate and heart rate, and is thus a boxer with one of the most intelligent tactics. On the other hand, Ippo, in front of his first defence match, not only is nervous but suffers progressively from fear and anxiety as he hears more about his opponent. Furthermore, Sanada Ikki's trainer was Hama Dankichi, the rival of Chairman Kamogawa when he was still active in the ring. Dankichi's special move in the days when he still fought, "Hien" ("Flying Swallow"), has been passed down to Ikki.Encouraged by the predecessors of the gym Ippo belongs to, Takamura and Kimura, his past opponent and his mother, watched upon by Kumi who he secretly has feelings towards, the date of the first defence match draws closer. Ippo versus Sanada, and the settling of the scores of the coaches, Chairman Kamogawa and Hama Dankichi, each of their thoughts crosses over, and now, the day of the decisive match arrives!Can Ippo dodge the "Hien" and find victory?