
Kamogawa, Nekota, and Dankichi as young adults.
Two years after the war while Japan was reconstructing after the war, Kamogawa, Nekota, and Hama Dankichi were prizefighters and close friends. Kamogawa and Nekota witnessed Dankichi being easily beaten by an American solider named Ralph Anderson in a match. When Anderson had his seconds throw items on the ground for the Japanese to pick up, they were enraged of the Americans looking down on the Japanese. Kamogawa and Nekota then spotted Yuki, who did not pick anything up as she believed she would be throwing away her Japanese pride.

Kamogawa finding out Yuki is from Hiroshima.
Later that night while talking about the differences of prizefighting and boxing, Kamogawa and Nekota came across Yuki again when she was being chased by Anderson and his seconds. With Kamogawa and Nekota protecting her, Miguel Zale translated for Anderson, wanting them to hand over the women as he believed that Japan's only entertainment is fighting men and devouring women. Angry, Kamogawa and Nekota attempted to beat Anderson, however, they were outclassed by his counters. Satisfied by the confrontation, Anderson left, and Miguel warned the Japanese that while Anderson does not represent the entirety of America, they should not seek vengeance as their prizefighting and his boxing are two very different things. Yuki then apologises for having them get hurt for protecting her. Yuki introduced herself and Kamogawa invites her to stay at his home after learning that she does not have a place to stay, with Nekota also tagging along. While there, she expresses her love of sunflowers and cooks for the two prizefighters as they train and fight, while Anderson fights and continues to look down on the Japanese. One day, when Kamogawa and Nekota return home to eat, Nekota starts showing signs of a sickness as he chokes on his food and drops a glass of water due to his hand going numb and shaking. Kamogawa then finds out that Yuki is from Hiroshima after she throws up blood due to radiation poisoning. She reveals to him that she moved to Tokyo wanting hope and energy, and seeing Kamogawa and Nekota fight gave her courage to live. Kamogawa allows her to stay at his home forever to let her enjoy the time she has left.

Nekota suffering from symptoms of Punch Drunk.
Later, Nekota returns home, gifting Yuki a dress and giving Kamogawa money to stop him from calling him a freeloader. Curious as to how he made money without fighting, Nekota reveals that he is a rickshaw driver. However, Nekota contently tips the rickshaw over during rides, gifts Yuki the same dress, and his hands keeps falling asleep, making him think something is wrong with him. After sparring with Kamogawa and avoiding all of his punches, he believes it is just temporary, and if he gives it time, he can go back to normal. Nekota then takes Yuki on a ride around Tokyo on his rickshaw. While riding, they come across Anderson beating another Japanese. When Yuki expresses her dislike of Anderson's fights, Nekota, not wanting to see Yuki looking down, asks if she wants to see a fight with strength left to spare, deciding that he will fight Anderson. Kamogawa and Dankichi discuss about Anderson, with Kamogawa not wanting to fight a battle he knows he would lose due to Anderson's weight class, noting how Japan's prizefighting will soon evolve into boxing with weight classes dividing further and new rules. However, they agree that Nekota would have the best chance against Anderson, though Kamogawa adds that taking punches from a larger sized man would break a person.

Nekota downs Anderson.
Nekota's symptoms get worse, but continues to hide it from Kamogawa and Yuki. When the sunflowers begin to wilt near Kamogawa home as Summer comes close to ending, Yuki hopes that she will be able to see them next year. Kamogawa mentions how it would make Nekota sad, as his feelings toward her are obvious, but Yuki stops him, asking if he noticed her feelings. As Kamogawa does roadwork, angered at himself as he does not want to betray the feelings of his best friend, Nekota returns home and reveals to Yuki that he will fight Anderson the next day, asking her to come watch and be with him at his home place after he wins as it would help her body through the radiation poisoning. The next day, as the match between Anderson and Nekota at the Kōdan Gymnasium is about to start, Nekota has trouble getting his bandages on his fist, but becomes stable enough when he arrives to the ring, wishing for Yuki to come watch the match. Elsewhere, Yuki tells Kamogawa that Nekota is fighting Anderson. Kamogawa shrugs it off until he learns about Nekota's strange actions as of late, concluding that he is Punch Drunk. Worried about his best friend, Kamogawa and Yuki rides to the Kōdan Gymnasium to stop him from any further injuries. When they arrive, they are shocked to see Anderson downed by Nekota on the third round. When Anderson gets back up, Nekota dodges his attacks while landing his own until the third round ends.

Kamogawa holding Nekota after losing to Anderson.
While Anderson wishes to not let the stars and stripes be tarnished no matter what, Nekota is glad to see Yuki watching him. When Nekota's second, Dankichi, tells Nekota to get ready, he discovers that Nekota was sleeping, which Kamogawa recognises drifting in and out of drowsiness as a key sign of being Punch Drunk. When the fourth round begins, Nekota immediately is in the advantage, leading Anderson to drop his boxer's pride and commit a foul by using the Rabbit Punch. Nekota is hit on the back of his neck and goes down. Worried about Nekota, as hits to the back of the head can cause brain damage, and can damage Nekota's already damaged body further, Kamogawa advises Nekota to quit. Nekota gets back up, wanting to end the match decisively so he can move to the mountains so that Kamogawa does not find out the reason he is Punch Drunk was because he fought a fair fight with him and plans to have Yuki move in with him along with a big white dog. Anderson proceeds to brutally beat a helpless Nekota until Kamogawa forces the match to stop by moving between the two, then holds Nekota out of the ring. As Anderson boasts about how no one in Japan can defeat him and mocks the Japanese, Kamogawa lets him know that his fists are willing to fight him.
Kamogawa and Dankichi takes Nekota to the Stone Hospital, where it is revealed that Nekota is in serious condition and that his damages will remain for the rest of his life. Kamogawa realises that he is the cause of Nekota being Punch Drunk, and wishes to dispel Nekota's regrets when he wakes up.