Continuing from the third episode, with no partner left, Kyūya decides to take the initiative. He first targets Honda’s partner. He tells Matsushita that Honda is a murderer and that trusting him would be dangerous. Kyūya suggests Matsushita verify this with Honda himself and proposes a deal: if Matsushita keeps him alive until the next round, he’ll know whether Kyūya is lying. However, Matsushita still lies about Kyūya’s suit and reports to Honda that Kyūya is the ❓J. Meanwhile, Yaba, the man from the couple, also warns that Honda might be the ❓J, as he was the first to encourage lying in the game.
Kyūya encounters Kotoko, the woman with Yaba, and mentions that he has no partner to check his suit. He asks if his suit is clubs, but Kotoko leaves without answering. From her reaction, Kyūya deduces that Matsushita’s earlier claim about his suit was false. Kyūya’s real goal is to shatter the trust between these two groups. Based on the reactions of Matsushita and Kotoko, he confirms that at least two of the suit claims are false—the rest relies on intuition.
In the end, Matsushita believes he has won, but observations from Kyūya, Honda, and Yaba all prove that Matsushita is the ❓J. Particularly, Yaba had told Kotoko the correct suit, yet she died, indicating manipulation. Kyūya reveals that Matsushita and Kotoko often went for snacks at the same time and even chose the same snacks each time—a method they used to communicate secretly.
They were pretending to be controlled partners, but in reality, Yaba, Kyūya, and Honda had been cooperating from the start, observing Matsushita. They adhered to the principle of trust, aiming to build reliance not through, manipulation, domination, brainwashing, coercion, deception, or fear—but through equality. Now, the three want to interrogate the ❓J, a citizen of Borderland, but they learn nothing. The ❓J, unable to bear the pressure, finally gives a random suit and commits suicide.
Arisu remains puzzled about what Borderland is trying to convey to them. He sorrowfully reflects that Kyūma’s fate seems to prove they can’t return to the original world—or perhaps that world no longer exists. He blames himself for sacrificing Tatta for such an answer.
Mizuki has a different perspective. She believes they can return to the original world and must continue playing for Tatta’s sake. The next day, she goes to find Kyūya, as they need more allies to defeat the Spades K. Each game cleared brings them closer to their goal. Arisu recalls how his friends used to treat his job-seeking struggles like the end of the world, and it makes him smile. Karube once encouraged him: "When life feels hopeless, just turn a corner—you’ll always find a way." But now Arisu wonders if he can truly find a way out, as everything seems impossible.
Lost in despair, Usagi tries to lift Arisu’s spirits by inviting him to hunt. Though they spend a long time without catching any rabbits, they finally break down emotional barriers and talk freely. Arisu becomes somewhat brighter. Suddenly, they hear strange noises and find everyone on the road dead. They encounter a dying man named Kameyama who whispers "film." Usagi finds a video tape in his camper van—he had been recording this world to uncover the truth.
In the footage, Kameyama meets Ann, who is studying changes in the river. She notices more fish and lush vegetation—the farther from the city center, the more primitive the scenery becomes. Ann explains that everyone arrived in this world at different times, but here, perishables decay the fastest, as if time itself is broken. She decides to go to the outskirts of Tokyo to uncover the truth about Borderland.
In a suburban area, a diverse group of people—men, women, the elderly, and children—have gathered. Most importantly, they all recall seeing fireworks before arriving, though no one remembers what happened that day. One woman mentions having brain surgery as a child, which helps her remember: that day, there were fireworks, but they might not have been real fireworks. Before she can finish, the Spades K arrives and begins a massacre.
At that moment, the Spades K appears. Arisu tries to lure him away, but strangely, someone else saves Arisu, separating him from Usagi. Who could have saved Arisu—and even known who he was? It’s Kuni.