While Kaiji is on medical duty, he meets the son of Ishida, Hiromitsu, who is also working underground for his debt, but blames his father for not bailing him out. Angrily Kaiji berates him for not accepting his own weaknesses. Later, Kaiji insults Ōtsuki who then makes life a misery for Kaiji and the Forty-fivers, but after three months they all return to full pay. Meanwhile, Kurosaki Yoshihiro, Tonegawa's replacement, observes Kaiji through CCTV. When the gambling night begins, Kaiji proposes no betting limit before he will join in and Ōtsuki accepts.

Kurosaki intervenes and tells Ōtsuki that he has no choice but to play, and in the end, he loses 18,252,000 perica which Kaiji splits equally between the Forty-fivers. Kaiji then asks Kurosaki to approve their requests for the one-day outside pass and he agrees. The Forty-fivers insist that Kaiji should keep the money and twenty one-day outside passes, leaving him with ¥800,000 (around US$7,800) to gamble for the team and pay off their debts. Now back in society above ground, Kaiji meets Sakazaki Kōtarō who is looking for a partner to win big in the illegal casinos. Kaiji accepts his offer, and is taken to an illegal casino where he sees a huge Pachinko machine called "The Bog". Each ball is worth 1,000 times more than normal and the jackpot is worth ¥550 million, more than enough to free Kaiji from debt.

Sakazaki ignores Kaiji's warning and continues sinking money into the Bog, while the casino manager gives instructions to initiate the 'block' which controls the flippers, stopping the balls descending into the winning zone. Although Sakazaki is close to winning he collapses and the casino manager, Ichijō Seiya, introduces himself and reveals that they are using brass balls today which are not affected by magnetism. They leave with a little more than ¥6 million after losing over ¥43 million in two hours. The next day, Kaiji spends hours back at the casino, staring at the machine, then goes to the staff room to cash in one ball he found, insulting Ichijō but also gathering information about the casino's operations.

On Kaiji's last day above ground, he challenges the Bog and Kurosaki warns Ichijō that Kaiji must have a plan, and Ichijō's reputation is on the line. Kaiji starts playing and more balls than expected drop between the pins and Ichijō is suspicious. It takes him some time to realize that Kaiji somehow entered the staff room and doctored the setting gauges for adjusting the pins so they were set wider apart. Panicking, Ichijō has the 'block' turned on, directing the balls away from the winning path.