"Tobi and the Duck" is the twenty first chapter in Ahiru no Sora.
Natsume challenges Sora to a 1-on-1 friendly basketball match and says that he will show him the national level of the sport. Since there is no basketball court nearby, Natsume draws a circle with a tree branch in the park's vicinity. The rules of the match are simple, one cannot step outside the circle, and if Sora can steal the basketball from him, Kurumatani will win. Sora agrees to the terms and informs if he wins, Natsume will join the basketball team. Kenji laughs at his condition and tells him that he is getting expelled. Kurumatani says it doesn't matter just agree to it.
At the start of the match, Sora tells himself that the rules of the match favor him because he is small in height and only needs to figure out Natsume's ball movements. Sora goes for a quick steal, Natsume reads his movements and does a crossover move. Kenji then confidently informs Sora that he is too slow, he should quit and, winning against him is out of the question. A furious Sora tells him he will never quit and then tries to steal the ball. The outcome of the match remains the same, and Sora's attempts remain futile. Kurumatani then tells himself that this small circle feels as though it was the entire court. Besides his speed, Natsume's basketball has a magnificent allegiance that attracts people's attention, and Sora understands why Momoharu was eager to get Natsume to join their team.
An exhausted Sora falls onto the ground and tells himself that he is nowhere near Natsume's level. The kids at the park try to cheer Sora and encourage him not to give up. Through their cheering and optimism, Sora regains his strength and motivation. He then informs those kids that he hasn't given up. Kenji notices that his expression has changed, and Kurumatani, this time, seriously tries to retrieve the ball and almost touches it. Natsume tells him to give up, and Sora refuses and encourages himself to put in a little more effort. While defending against Sora, Kenji reminisces his time with his father and how he got into playing basketball. During that moment, Sora steals the ball from him. Afterward, the advisor, Satsuki, arrives and informs Kenji that he has been expelled. During that moment, Nabe, Yasuhara, and Masahiro arrive with the senior students; the day before, Kenji fought. They informed Satsuki that Natsume shouldn't be expelled and should listen to what these students have to say.