Karil is a non-recurring character in Hajime no Ippo.
Years after opening his gym, Karil's acquaintance, Kawabe introduced him to one of his students, Sawamura Ryūhei, while warning him that Sawamura has a bit of a anger problem. While Karil noticed that Sawamura had more than a bit of an anger problem, he felt a spark inside Sawamura and believed that Sawamura would give him his first title for the gym.
When Sawamura Ryūhei came back to the gym, Karil panicked after seeing Sawamura's hand cut up, thinking that Sawamura was in another fight, however, Sawamura implied he wasn't. Karil informed Sawamura that he has sent a request to the Kamogawa gym to fight the JBC featherweight champion Makunouchi Ippo, and should receive a reply soon. Looking at Sawamura's hand, he became nervous after seeing teeth marks. In a plan to fight Ippo, Karil had a junior welterweight from another gym spar against Sawamura. While he felt he should kick Sawamura out after he kicked the sparring partner, Karil was amazed of Sawamura's strategy to go against the Dempsey Roll. Karil had trouble finding anymore sparring partners due to Sawamura always leaving them injured. Karil got excited when Sendō Takeshi arrived at the gym to spar, however, Sawamura declined the request due to Sendō's relationship with Ippo, so instead they head out to talk, leaving Karil hoping that they don't fight. Later, Sawamura asked Karil to do mitt-training while he is out of breath, which Karil acknowledged as Sawamura training to go against Ippo's high stamina, being pleased to see Sawamura's determination.
During a public spar, Karil explained Sawamura's Bullet and Flash to Fujii Minoru, while being afraid that Sawamura's match with Ippo may end in a disqualification due to Sawamura's weight management turning him into that of a starved mad dog. Karil arrived with Sawamura to the Kōrakuen Hall for his weigh-in against Ippo. The next day, Karil was Sawamura's second for his match against Ippo. After the first round, Karil warned Sawamura to not cheat and to wait for a chance. Sawaura purposely undid the taping on his glove in the second round, leading the referee to pause the match for Karil to tape it back up. After the third round, Karil informed Sawamura that while Ippo may look hurt, he has the tenancy to defeat his opponent when they think he is in pain, advising for Sawamura to not rush it. After the fourth round, Karil mentioned to Sawamura that after he defeated the Dempsey Roll, the light left Ippo's eyes, making the fight being theirs close, still warning him about a possible comeback. After the fifth round, Karil believed that the problem child Kawabe gave him will become the Japanese champion. After Sawamura lost in the seventh round, Karil called for a stretcher so that he could go to the hospital. Karil went to the Inoue Emergency Hospital where Sawamura was taken and was informed of the injuries Sawamura received.
Sawamura moved to the junior lightweight class and had an upcoming JBC title match against the JBC junior lightweight champion, Mashiba Ryō at the Champion Carnival. Karil went to the Kōrakuen Hall to attend Sawamura's weigh-in with Mashiba. The next day, Karil arrived to the Kōrakuen Hall to be Sawamura's chief second in his JBC junior lightweight title match against Mashiba. During the second round when Sawamura and Mashiba were on equal ground, Karil acknowledged Mashiba's experience, assuming that he must have fought a counter user that is on Sawamura's level before to be able to dodge his attacks. After the second round, Karil advised for Sawamura to slowly put on the pressure and wait for his chance, however, Sawamura expressed his dissatisfaction in doing so. During the third round as Sawamura and Mashiba were brawling with illegal blows mixed in, he knew that Sawamura was trying to take the pace with the illegal blows and force Mashiba to have a brawl, however, he sees that Mashiba is good at brawling as well. After the third round, Karil mentioned to Sawamura that he is impressed that he was able to turn the match around, as Mashiba won't be able to recover from the damage before the fourth round begins. As Sawamura left for the fourth round, Karil instructed to keep calm and to not rush it. After the fourth round, Karil ordered Sawamura to not let Mashiba run and recover, and to act as if he is finishing the match in the fifth round. After the fifth round, Karil told Sawamura to remember that when he is in pain, that Mashiba is as well, and that he will become champion if he makes it through. One of his fellow staff members were worried about Sawamura, Karil figured that Sawamura is slipping in and out of consciousness, but noted his dedication to get the belt is something that he has never seen him do before. Karil watched in shock in the sixth round as Sawamura was getting hit until he was knocked outside the ring while the referee had the match paused. The referee disqualified Mashiba, making him lose, and Sawamura the new JBC junior lightweight champion.
Karil left with the venue's doctors as Sawamura was sent out to the venue's doctor's office on a stretcher. At the doctor's office, Sawamura received a checkup by the doctor, and was revealed to be fine to not go to the hospital, however, the doctor recommended for him to be under Karil and Kawabe's watch and for him to see a brain specialist. At Sawamura's room in the venue, he was given the JBC junior lightweight champion belt by the Tōhō coach. After he gave the champion belt to Sawamura, Sawamura left the room. Later, his staff members urgently informed Karil and Kawabe that Sawamura and his motorcycle are gone. Sawamura got in a motorcycle accident and was sent to the hospital with injuries that forced him to retire from being a professional boxer.
He has black hair, he is short and wears always a purple shirt, when his boxer's fight and usually in the gym. He is a friend of Sawamura's teacher.
- Karil's name is from the Karil Fishing Shop that sells "Sawamura" brand fishing gear by "Yukihiro Sawamura," where Sawamura got his surname from.
- Chapter 494, page 10