Kumi Mashiba - 間柴 久美

Is Ryo Mashiba's sweet-natured, but hard-working and willful younger sister, and as such understands him better than anyone else. She will do almost anything to support her brother and make him happy, including going to his matches even though she doesn't like to see him get hurt. Ippo becomes infatuated with her early on, but didn't have a chance to tell her until more than a year later, when they met in an hospital as patient and nurse some months after the Ippo/Mashiba ring.

They become friends and Kumi comes to like Ippo back, but their relationship tends to suffer from their friends' and relatives' constant interference, and also was somewhat strained after Ippo thought she was smitten with Dr. Sanada, until Kumi herself clarified the mistake after their match but didn't get a chance to say that Ippo was the one she really loved. Kumi tends to be modest and shy, but she will stand up for her brother and friends at a moment's notice. Voiced by: Sanae Kobayashi, Yuka Hirata (New Challenger).

Ichiro Miyata - 宮田 一郎

Voiced by: Tomokazu Seki

Miyata a very skilled outboxer that specializes in counter punches. Considered by many to be a boxing prodigy, he uses the boxing style that his father used. After his father is forced to retire, Miyata decides to take on his style of boxing to prove its worth, and to go above and beyond him. He begins at Kamogawa Gym, but after losing to Ippo, he later transfers to Kawahara Gym in hopes of one day facing Ippo in an official match. Miyata himself looked down on Ippo a little at first, but after he helped Ippo to buy new boots for their first match, he started to respect him more, developing a friendly rivalry.

Miyata originally starts to rise very rapidly in the Eastern Championship, until he is defeated by Ryo Mashiba. After physically recovering and graduating high school, he visits Ippo and tells him that he's going in a tour through Thailand and Korea to improve his skills and then fight him. Miyata has trained all across the Pacific and eventually returns to the mainstream boxing scene as the main contender to the OPBF featherweight title. Together with the Jolt Counter, a deadly full-body powered counter blow enough to knock someone out cold, Miyata KOs Australian boxer Arnie Gregory to become the current regional champion. He has defended his title five times, all by KO, boosting him up to the rank of WBC #5 Featherweight. Miyata currently defeated Randy Boy Junior, the OPBF interim champion who was crowned during Miyata's absence due to broken fists. Successor of the style that defeated his father. His ring name is the God of Thunder due to his quick speed,and his powerful counters.

Unfortunately Miyata's body structure is not suited for Feather Weight Class but for the Junior Light weight & light weight class, due to that he needs to fight a single match per month to keep his weight at 126 Lbs, the limit of the feather weight class. Furthermore he has a glass jaw that is a severe weakness for him. Miyata seems partially based on former world champion Sugar Ray Leonard for his phenomenal skill, speed, and counter punching ability, though Morikawa has said in interviews that he also based Miyata on his personal friend, Naoto Takahashi, a former Japan and OPBF champion.

Miyata currently holds a record of 22-1-1 with 22 Knockouts and is the reigning OPBF Featherweight Champion.

Tatsuya Kimura - 木村 達也

Ippo's senpai and Aoki's best friend. He is the smooth, collected type and a romantic at heart, but trains as hard as anyone. His style incorporates a fast left and faster footwork and is considered by Miyata to have "no weaknesses" yet, it also doesn't have strengths either which creates Kimura's weakness. In the OVA, which was dedicated to Kimura, he is in training for his bid for the Japanese junior lightweight championship against Ryo Mashiba, he developed a devastating vertical combination known as the Dragon Fish Blow, which Kimura learned while watching his pet fish jumped up and eat his meal in front of him. Another interesting fact is that, out of all the opponents that had fought Ryo Mashiba, Kimura is the only one Ryo had feared during a match. In the past, he and Aoki were the toughest high-school thugs around, but now Tatsuya's real job is at his family's flower shop. His current record stands at 24 Matches 16-5-3 (W-L-D), with 8 KOs, and the best rank he reach is 3rd in Jr. Lightweight, because the 1st & 2nd resigned from fear of Mashiba.

Kimura is ranked 7th in the JBC Jr. Lightweight rankings. After losing to Ryo Mashiba, he announced his retirement from boxing. Shortly after, unable to stay away from boxing, he returned saying he'd spell his name in katakana (タツヤ, Tatsuya) instead of kanji (達也,, Tatsuya). Kimura's character seems to be at least partially based on former world champion "Fearless" Freddie Pendleton, who had been a journeyman fighter his entire career, yet was still able to fight on even terms with some of the best in the world with his high level of skill.

Voiced by: Keiji Fujiwara (Japanese), Grant George (English)

Masaru Aoki

(青木 勝, Aoki Masaru?) is Ippo's senpai and Kimura's best friend. Aoki provides much of the gym's comic relief and exercises one of the world's most unusual fighting styles. A few of his signature techniques include the fan-favorite Frog Punch, double punch, an untorqued (ineffective) corkscrew punch, and the utterly ridiculous Lookaway (which has also been adopted by Takamura). In the past, he and Kimura were the toughest high-school thugs around, but now Aoki's real job is at a ramen restaurant. Due to the numerous times being dumped by the pretty girls in high school, he's developed a taste for women with unattractive faces. He has fought for the Japanese lightweight championship and shares an apartment with his girlfriend, Tomiko, a friend of Kumi Mashiba whose nice personality and good body more than compensate for her less-than-stellar face. Aoki seems to be based on either former world champion Jorge Paez, or hardcore fight fan hero Emanuel Augustus for their offbeat fighting styles and records. His current record stands at 20 Matches 10-6-4 (W-L-D), with 6 KOs, and the best rank he reached is 1st in Lightweight. His signature "Look Away" technique is based on a skill former World Middleweight Champion Jake LaMotta had used in his career.

Aoki is ranked 7th in JBC Lightweight rankings.
Voiced by: Wataru Takagi (Japanese), Jim Taggert (English)

Mamoru Takamura

(鷹村 守, Takamura Mamoru?), voiced by Rikiya Koyama (Japanese) and Eddie Frierson (English), is a strong boxer that has never lost a match. He has an incredible athletic ability that manifests through his strength, speed, stamina, and reflexes. Takamura also has an insatiable appetite for women, which is only overshadowed by his obsession for victory. At one point, he single-handedly knocks out an adult bear while sustaining gashes on his arm, and more notably on his chest. The weakened bear is eventually killed, and he is dubbed "The Bear Slayer". He honors the moniker by wearing the Bear pelt, bear-ing (PUN intended) his scars proudly.

He originally was a delinquent that often got into fights. Because of his strength, he often left his victims with serious injuries. He was disowned by his family due to a brawl initiated by himself which happened during a rugby match where his older brother was competing and fans booed. By the time the brawl was over, at least 20 people were injured. After the incident, Takamura continues to fight until he meets Coach Kamogawa. After weeks of training, and without a single sparring session, Takamura defeats his first opponent 25 seconds into the first round. He works his way to becoming the JBC Middleweight Champion, and then moves on to become the WBC Junior Middleweight Champion, and then the WBC Middleweight Champion (which makes him the only current World Champion from Japan). His current aspiration is to conquer the next 4 classes up through heavyweight, but first he must win his upcoming fight for a Super Middleweight Championship. Takamura's character resembles former Middleweight Champions Sugar Ray Robinson, Marvelous Marvin Hagler and Roy Jones Jr. for his versatile repertoire of punches, his ability to box and brawl at any range, and his uncanny physical giftedness.

As a two-time World Champion and former Japanese Middleweight Champion, Takamura is the former WBC Jr. Middleweight Champion, and the reigning WBC Middleweight Champion.

Ippo Makunouchi

(幕之内 一歩, Makunouchi Ippo?), voiced by Kōhei Kiyasu (Japanese) and Steve Staley (English), is the main protagonist of the series. He lives with his mother, Hiroko Makunouchi, and helps with the family charter boat fishing business. When he was young, Ippo use to get bullied and picked on by others in his school. As fate would have it, Takamura came upon Ippo as he was getting a beating from a couple of bullies and decided to help him. Takamura saw something in Ippo and introduced him to the world of boxing. After seeing a video of Mike Tyson, Ippo becomes inspired to take up boxing to feel reborn with strength, as a sort of therapy and asks Takamura to get him into Kamogawa Gym. Immediately after arriving at Kamogawa Gym he impresses Takamura and Kamogawa with his explosive punching power and guts in the ring. Like he has with Takamura, Kamogawa personally takes on Ippo as his pupil and starts him on the path to being a pro boxer. Since then, Takamura has treated Ippo like a younger brother and has taken him under his wing.

Ippo is a classic in-fighter and is well known for his Peek-a-Boo style of boxing and hard punches including three signature punches: a rib-cracking Liver blow, Gazelle punch (an uppercut variant), and the Dempsey roll technique. During his match with Sawamura, he modified the Dempsey roll to prevent it from being countered. He also modified the Dempsey roll into a "smash" version when he fought against Jimmy Sisfa, a.k.a. "Scratch J". His signature punches are modeled after Mike Tyson, Floyd Patterson, and Jack Dempsey respectively. Although he is not a technical boxer, Makunouchi makes up for it with his superb fighting spirit. His nickname is the God of Wind, coined after the force of his powerful blows. Ippo is based on Mike Tyson.

Ippo's current record as a professional boxer with 22 matches is 21–1–0 (W-L-D), with 21 KOs, he is the reigning JBC Featherweight Champion, having defended his Japanese title 7 times, and holds a single digit ranking in the WBC.