Isamu Akamatsu (赤松勇, Akamatsu Isamu) is a semi-recurring character in Hajime no Ippo.
Isamu is a close friend with Kizakura Hiroshi and they both joined Kamogawa Boxing Gym after Aoki Masaru's first title match and made him not retire. These three together make the "Aoki Team" with their leader, Aoki. Isamu partakes in boxing training at times and helps Aoki at the Chūka Soba
His surname is Akamatsu. In Japan, surnames are listed before given names.
Inspired by Aoki's JBC lightweight title match against Katsutaka Imae, Isamu and his friend, Kizakura Hiroshi, encouraged their idol, Aoki to not retire when he was on the brink. Isamu and Hiroshi went with Aoki to the Kamogawa gym to be introduced to the gym members. As Isamu only follow Aoki's orders, he ignored Takamura Mamoru's order of getting him juice until Aoki told him to do it. While Isamu and Hiroshi were sitting around the gym, they were dragged into doing roadwork with Itagaki Manabu and Kimura Tatsuya. As Isamu and Hiroshi were having trouble running, they revealed how hard their past and only like the scent of Aoki because he wins without trying. When Aoki arrived to the group, Isamu and Hiroshi ran to him for comfort.
Isamu went to the Ryōgoku Kokugikan for Takamura's first WBC junior middleweight title defence against Larry Bernard. Isamu, Hiroshi, and Aoki were kicked out by the venue's staff due to them trying to cheer with instrument. In the anime, they did not play instruments, and Isamu and Hiroshi instead expressed how there is a smell of an easy win. After Takamura's win, Isamu ran away with Hiroshi and Aoki due to Aoki being blamed for Takamura getting hit after using the Look Away. Later, since Makunouchi Ippo needed help reviewing his fifth JBC featherweight title defence opponent, Sawamura Ryūhei, Isamu was one of the gym members to be called to Takamura's home to try and help Ippo. The event ended when Takamura got angry due to the large number of people in his room.
When Isamu was walking with Hiroshi, Hiroshi dropped books next to Itagaki containing information about techniques that he and Isamu were gathering, Itagaki grabbed them as he was seeking information about the Dempsey Roll. While nothing was in it of useful information, when Hiroshi held out his hand to grab it from Itagaki, he startled Itagaki which sparked an idea to Itagaki about the Dempsey Roll's methodology and the books were thrown back to them. When Alexander Volg Zangief visited the Kamogawa gym, Isamu and Hiroshi had Volg polish the Statue of Takamura before getting scolded by Itagaki for it.
When the Kamogawa gym members' matches arrived, Isamu and Hiroshi went to the Yokohama Arena. While Kimura was fighting Eleki Battery, the two gave details about Kimura's situation throughout the match. They also brought Tomiko to Aoki's room in the venue to cheer him up. Isamu and Hiroshi wished Aoki good luck, however the two thought that even if he loses, remembering Takamura's bet of giving Aoki Papaya Dachiu's haircut if he loses, it would still be good. When Aoki's match against Papaya began, Isamu watched and cheered for Aoki. During the match, Isamu and Hiroshi could smell that Papaya has the same odour as Aoki. Isamu watched as Aoki's match ended in a draw. When Miyata Ichirō was having his fourth OPBF title defence against Medgoen Dachboy, Isamu and Hiroshi reported to Aoki that Miyata was still fighting in the fifth round. making Aoki leave his room to watch in the audience area.
After Takamura won against WBC middleweight champion David Eagle, Isamu followed everyone as they went to Takamura's house to make sure he went to sleep. Isamu and the others were thrown out as Takamura was unable to sleep with everyone watching.
When Aoki's hairstyle was forcefully cut by Takamura to be like Papaya's, Aoki gained popularity after using the new haircut, which looked like broccoli, to star in a commercial advertising broccoli as "Broccoman." To support Aoki, Isamu and Hiroshi cut their hair just like his and wore the trademark t-shirt. Isamu and Hiroshi arrived to the gym with Aoki to show Takamura how Aoki's Broccoman brand has grown, causing a fight between Aoki and Takamura. to see who is more popular.
Akamatsu is seen wearing a red and purple striped long sleeve shirt and long black pants.