"Adversary" is the fifty seventh chapter in Ahiru no Sora.
The friendly sports competition at Kuzuryu High has begun, and the first, second, and third-year students of Kuzuryu High are participating. The athletic competition includes sports like baseball, soccer, basketball, badminton, volleyball, and many more. Chiaki’s class is participating in a friendly baseball competition. Hanazono is the ace or starting pitcher of his team, and due to his immense strength and power, Chiaki viciously strikes out the opposing team’s batters. Upon receiving Hanazono’s pitch, his own team’s catcher gets knocked out cold, and his colleague then requests for replacement. Chiaki is confident that his popularity among females at Kuzuryu High will substantially rise if his class wins the baseball tournament. The opposing teams’ batters are scared of confronting Chiaki’s pitch.
Nabe comes forward as one of the batters from his class and challenges Hanazono. A confident Chiaki states to Nabe that if he can hit a home run on his pitch, he will give him his 1000 funbucks, referring to the proprietary currency that is used in certain good stores or venues to purchase items or services in replacement of genuine money. This currency is commonly used in theme parks or buying online games with a "cash store." Nabe then insists that 1000 funbucks seems a bit low; let's make the wager to 5000. Chiaki agrees and throws one of his vicious pitches; a confident Nabe swings the bat. Due to Hanazono's pitch being a bit too powerful, the bat breaks. Nabe then switches to a metal bat. A confident Chiaki throws his ferocious pitch, and Nabe hits a home run. Chiaki’s team loses, and Nabe’s team wins the match and the wager of 5000 funbucks.
Meanwhile, at the school’s basketball court, a cheerful Nao watches all the matches. Kenji displays his efficient basketball skills on the court. One of the seniors in the opposing team, out of jealousy, tries to hit Natsume. Kenji sees and easily avoids it and scores the layup. Natsume’s team win by a significant margin, with a score of 12 to 4. All the girls at Kuzuryu High praise Natsume for his good looks and his efficient basketball skills. On the other side of the court, Sora’s class is also participating in the basketball competition. Sora is his team’s point guard. Nao notices that Sora is working on trying to adapt to a point guard role. At first, Sora struggles, but later, he makes some amendments and, instead of going on offense, he focuses on passing the ball to his teammates, who then score. Sora's team also advances in the next round, and upon watching a furious Natsume tells Sora that if he had passed the ball to him similar as he did in this match, their team would have won the practice game against Kitasumi High. Upon concluding, a confident Natsume vows that he will not be defeated again by any other team or player, referring to Sora.