J: Solitary Confinement
Rules:
Players must correctly identify the suit displayed on the back of their own collar. Since the suit is on the back, players cannot see their own. Each round lasts one hour. Five minutes before the end, players must enter their cells and declare their suit. Those who fail to identify their suit correctly are eliminated. When time runs out, the collar will detonate, killing the player. The suit on the collar changes every round.
Solitary Confinement tests the players' trust in each other. Additionally, the Heart J (the opponent) is hidden among the players. The game ends the moment Heart J is eliminated. Each round lasts one hour. During the game, players are forbidden from using reflections or cheating to discover their suit, nor can they use violence or weapons to harm others. This means the game will not end unless Heart J answers incorrectly and dies. Players must deceive Heart J to clear the game, so the game could continue indefinitely. Visa countdowns are temporarily paused.
Continuing from the second episode, Arisu reflects on Tatta's always optimistic and encouraging nature. Tatta used to be a car mechanic but was often seen as clumsy and inexperienced by his seniors. He didn’t want to end up like his father, who worked himself to death, so he dreamed of saving enough money to study English. However, his coworkers mocked him, saying he couldn’t do anything right and shouldn’t aim so high. He wanted to do something that would make others grateful. The next day, Tatta accidentally caused a severe injury to a senior colleague, leaving him permanently unable to work. Everyone blamed Tatta.
Back in the game, with only minutes left, Tatta decides to make a different choice. Arisu discovers Nira assaulting Usagi and angrily intervenes, rescuing Usagi and returning to the base, only to realize Tatta is missing.
Arisu rushes to the beach to find Kyūma, hoping to learn the truth about the game. But Kyūma believes Arisu has already given up, so there’s no point in telling him. Arisu asks to shake Kyūma’s hand before dying, as he has come to understand Kyūma’s philosophy of listening to others and giving them time. Even though they are opponents, Arisu wants to thank Kyūma for toturing him this lesson. Kyūma sees no harm in a handshake, but this act allows Arisu to reverse the points. Earlier, Tatta had planned to remove his wristband—he wanted Arisu to secretly use it to deceive the enemy, since the rules never stated that wristbands couldn’t be removed. Thus, Arisu breaks Tatta’s hand to retrieve the wristband, fulfilling Tatta’s final wish to be thanked.
Kyūma is utterly impressed by Arisu’s unexpected ruthlessness. Arisu realizes that Kyūma and his team were once players too. Kyūma’s carelessness doesn’t anger his teammates; instead, they are grateful to him for keeping them alive until now—they have lived fiercely. Arisu wonders if clearing the games only means becoming "citizens" of Borderland rather than returning to the original world. Kyūma only offers a vague answer: "If you believe that, then it must be the truth." He believes the choice lies entirely with Arisu. Their meeting in this game destined one side to die, but Kyūma considers Arisu a friend and wishes him meaning in survival.
Meanwhile, Tatta is bleeding out and losing consciousness. Hearing Arisu’s final thanks, he dies with no regrets. The group buries Tatta by a beautiful waterside, vowing not to let his sacrifice be in vain and to strive forward including his share. Although Nira is frustrated at being saved by Tatta, he acknowledges his survival and grudgingly thanks Tatta for his sacrifice.
Elsewhere, in Teion Prison, another ❓J game is underway. Players wear collars and gather in a central monitoring room. Kyūya is among them. This game requires deceiving the ❓J to end it; otherwise, players are trapped forever. The game’s essence is to pit 20 players against each other in mutual slaughter until ❓J is eliminated, fostering distrust since anyone might deliberately give wrong answers.
Suddenly, a girl suggests forming teams to prevent lying. Kyūya explains that to win, players must observe others to see who is less likely to lie and who has unbreakable trust bonds. Several rounds pass with everyone surviving, but this means the game could last forever unless ❓J starts killing. Soon, someone begins lying, firing the first shot of deception. The person who tricked a troublemaker is immediately suspected of being ❓J, and someone proposes killing the liar. Everyone agrees, though some feel uneasy about their own lies.
The accused boy isn’t ❓J. The group descends into chaos. A woman in a blue dress manipulates them to target others one by one. As more people are eliminated, trust erodes further, and everyone starts lying to survive. Eventually, only a few remain. Kyūya and his partner check each other’s suits, but his partner, too kind for the game, chooses to die by quitting. This leaves Kyūya alone.