Ippo Makunouchi is a shy young man who works with his mother, Hiroko on their fishing boat business while he attends school, so he has no time to hang out with friends. One day, as Ippo is walking home, he is approached by Masahiko Umezawa and two other bullies. They start beating him up and make fun of him and his mother. Suddenly, a jogger walks by and scares the bullies away. Ippo loses consciousness so the jogger takes him to the boxing gym where he works out in and heals his injuries. When he wakes up, Ippo is amazed by all the boxers working out. The jogger then test tries to get Ippo to punch a punching bag with the bully's face drawn on it. Even though his hand gets bruised, the jogger notices Ippo has a very strong punch. He gives him some world championship boxing tapes to look over and sends him home. Inspired by the tapes, Ippo seeks out the jogger, Mamoru Takamura, who is a middle-weight professional boxer, and begs him to train him in order to fulfill his dream of becoming a professional boxer. To test him, Takamura kicks a tree and catches many leaves in his hand, using his lightning-fast jabs. He tells Ippo that if he can do the same, he will train him.

Ippo's goal was to catch 10 leaves, with only a week to do so. While balancing school and work, Ippo also practiced his jabs. Finally, he figured out not only to increase the speed of his jabs, but also caught all 10 leaves in his left hand. Impressed, Takamura then assigns Ippo to work out his muscles, body and running speed for one month. Once done, Takamura takes Ippo back to the gym to test out his skills. His first test was to spar with a rookie the same age as Ippo, Ichiro Miyata.

At first, it seems that Ippo could not keep up wuth Miyata, given the fact that the latter is more experienced. Ippo keeps taking hit after hit and gets knocked down twice. After receiving some advice from Takamura, Ippo keeps getting back up to fight. To everyone's surprise, Ippo keeps absorbing Miyata's punches. Suddenly, Miyata hits Ippo's chin, causing his brain to move back and forth. However, Ippo was able to keep up with Miyata's movements, but unfortunately lost to Miyata's superior skills. However, the owner of the gym, Genji Kamogawa, was impressed by Ippo's determination and decides to train him every day in the gym.

Ippo finally begins his training in the gym. First, Kamogawa himself, helps Ippo to focus on his jabs and the one-two technique. After getting the hang of it, Kamogawa instructs Ippo to practice shadow boxing. Though some patrons in the gym show him how to do it, Ippo tries again and again. However, as he watches Miyata sparring, he starts to finally understand how to shadow box. Takamura and Kamogawa realize what a great talent Ippo has, but Miyata feels jealousy towards him.

Ippo begins training with coach Kamogawa for about three months in order to prepare for a rematch with Miyata. During that time, he begins working on more techniques. Also, he learns more about Miyata's father, who was a former professional boxer who believes in skill surpassing power. However, in his final match, he lost and realised that that power surpasses skill. Since then, Miyata is trying to prove that his father's way of boxing is correct. After more training, Ippo is finally ready for his rematch with Miyata.

A representative from a boxing magazine comes to Kamogawa's Gym on the same day Ippo and Miyata have their rematch. With Takamura as referee, the rematch begins. Both fighters begin their four-round match, each displaying their progress during the last three months. Each one knocking each other once, taking their audience's breath away.

Ippo and Miyata are in the last round and Ippo does a short upercut to Miyata's chin, Miyara was knocked down and was unable to get up, Ippo wins the rematch.

Ippo trains with Takamura and discovers the hardship of pro boxing.

Ippo takes the License Test and meets Mashiba.

Ippo and his opponent Yusuke train for Ippo's debut match

The four round match finally begins. Each fighter delivers harsh blow after harsh blow, with their teams shouting advice. Miyata arrives secretly to watch the match. However, Oda's hook actually cuts Ippo's left side of the face around his eye. The doctor warns him that if he bleeds again, he will lose with a technical K.O. Unwilling to let that happen, Ippo goes all out to take out Oda, and he does with his most powerful jabs, earning him victory. In the locker room, Oda swears to continue training and Keiko, having forgiven him, urges him to continue working hard. Ippo and his friends celebrate after the match.

Ippo's second match is against Yoshio Fujigawa. However, Umezawa and his two friends actually go to Ippo's match to cheer him on. After working on a new guarding technique, Ippo seems to be on top. However, his opponent starts to play dirty by cheating. But, Ippo's determination allows him to fight back and break his opponent's guard with a mighty uppercut. The next day, Umezawa decides to become Ippo's friend and tells everyone about Ippo's mighty victory.

The Rookie Championship is about to begin. Ippo's first opponent is an American soldier, Jason Ozma, who is based in Japan. To prepare for the match, Ippo trains with Takamura while practicing to dodge hooks and uppercuts. Ozma, on the other hand, trains for the people he came to know in the Japanese gym where he was based.

Ippo and Ozma begin their match. Both of them give powerful blows, each surprising one another. Each boxer tries to think of a strategy to take out the other, until Ozma knocks Ippo down. After a brief moment, he gets up and each counter with a punch to each other's face. The intensity of the match continues.

The match continues between Ippo and Ozma, with each fighter dealing one crushing blow after another. Oma manages to knock Ippo down, and it looked like he was down for the count. However, Ippo managed to get up and continue the assault, following his coach's advice on pretending like he feels no pain. Ozma is then knocked down himself. He manages to get up as well. As the fighters continue, Ippo receives one crushing blow after another, until he ducks and gives a huge uppercut to Ozma's chest, knocking him down. Ippo wins his first tournament match and thanks Ozma for the incredible fight. Ozma wishes him luck for his next matches. Both boxers receive applause and praise from the audience as they leave the ring.

Ippo and Takamura, along with a girl that Ippo has a crush on, sees Miyata's match. Miyata completely lowered his opponent's guard and quickly took him out. Afterwards, Ippo and his friends at the gym saw some videos of some of the next opponents he would face in the tournament. Later, after meeting the girl at a bakery where she worked, Ippo received a call from Takamura about a training camp for preparation for his next match.

Ippo, Takamura and their two friends from the gym, Aoki and Kimura go to training camp, which also involves fun at the beach. After sunset, the gang of four start running and practicing shadow boxing at their hut. Ippo also learns about movement with his feet from Takamura, which happened to be Ippo's weakness. After a fireworks celebration, all four boxers head home.