Keys and Knives

Following the end of the attempted mutiny, the Masked Soldiers begin massacring the surrendered X-voters. No-eul discovers Gyeong-seok among the rebels and shoots him non-lethally, before telling him to play dead. Pretending to have changed her mind about their operations, No-eul has the organ-trafficking Masked Men take her to their operation room, but just as they're about to start extracting Gyeong-seok's organs, No-eul kills three organ traffickers and forces the survivor, the group's doctor, to treat Gyeong-seok's wounds instead.

At the dormitories, Gi-hun wakes up and learns about the rebellion's failure, with Hyun-ju and Dae-ho being the only ones besides him to avoid getting executed due to being in the dormitories when the revolt was being suppressed. Broken over once again leading many others their deaths, yet being still alive himself, Gi-hun gives up on trying to stop the games, while blaming Dae-ho for chickening out and failing to bring the ammunition, which led to the rebellion's failure. With most of the X-voters dead, the games continue, and the next day, the players are divided by random into two groups: red and blue. The game is Hide and Seek: the goal of the red players is to navigate throughout the labyrinth to find and kill at least one blue player within 30 minutes, and if they fail to do so, they'll be eliminated; the blue players must subsequently avoid getting caught and killed until the timer runs out, while also being given three types of keys that can open the doors in the labyrinth, including the exit, which requires all three keys. Before the game begins, the players are allowed to switch their positions with someone, with Myung-gi and Yong-sik becoming taggers in place of Jun-hee and Geum-ja, respectively.

Meanwhile, Jun-ho's party discover that the drone operator fell overboard last night, unaware that Captain Park, who's Front Man's mole, killed him and disposed of the body in the sea afterwards. As they return to the mainland to replenish their supplies and find a new drone operator, Woo-seok, who starts to have suspicions about Captain, decides to stay to search for any information about him, while Front Man reluctantly orders Park to kill the search party, including Jun-ho, if he's no longer able to keep the island's location secret long enough for the competition to be over.

Tropes:

• Anti-Frustration Features: Hiders in hide-and-seek don't need to find the exit to win, just survive until the timer runs out.
• Blame Game: Both Gi-hun and Dae-ho blame each other for the failed revolt. Gi-hun blames Dae-ho for not bringing the magazines that would've given the rebel team more ammo in fending off the soldiers. Dae-ho rebuts that none of the rebels' deaths would have happened if, instead of engaging in a revolt, Gi-hun had just followed his friends' advice and killed the O-team first during the night riot to ensure the X-team wins the vote and everyone goes home.
• Blue Is Calm: Invoked together with Red Is Violent. The Blue Team are the hiders in the fourth game, who must evade the Red Team's attempt to kill them by either finding an exit or hiding until the clock runs out. They are only given keys to open the doors in the play area and aren't given anything to fight back.
• Chuck Cunningham Syndrome: Player 348, one of the few minor O voters with speaking lines, was last seen having survived the special game, but he is nowhere to be seen during the fourth game. Despite this, the guards state that there are 60 players participating.
• Dead Guy on Display: The dead bodies of Gi-hun's rebels, except for Gyeong-seok's, are hanged on the main hallway for all the remaining players to see, as a warning against any further revolt attempts.
  "Players, what you see before you here is the fate of those, who refused to accept the results of our free and democratic voting process by attempting to forcibly put an end to the games through violent means. Let us be clear — we will not tolerate any further irrational behavior or attempts to violate the fair, just, and clearly outlined rules of these games. Such actions will be punished in accordance with our strict regulations. We would like to thank you all for your understanding and cooperation."
• Despair Event Horizon: Gi-hun tries to get the guards to kill him after he's the only one spared in the failed rebellion, and after that spends the rest of the time chained to a bed, barely able to bring himself to move, let alone bother voting. Learning that Dae-ho chickened out motivates him with anger, at least.
• Developer's Foresight: The rules of the fourth game state that each member of the red team must kill at least one person from the blue team to pass, explicitly opening up the opportunity for a red team member to kill more than they need to in order to increase the winnings pool and shut out other red players.
• Heroic Sacrifice: Myung-gi, sincerely according to Word of Saint Paul, offers to let Jun-hee kill him so she can pass the 4th game. She opts to switch instead.
• Hide-and-Seek Horror: The fourth game is hide-and-seek, except the taggers are given knives to hunt down and kill the "hide" team, whom must find the exit or survive until the clock runs out to win. The taggers don't fare much better either; if a tagger fails to kill anyone from the hiding team within the time limit, they will be eliminated instead.
• Hunting the Most Dangerous Game: The fourth game is "hide-and-seek", but with a twist. The hiders are unarmed, but are given keys that allow them to progress through the maze and eventually exit; however, any doors they unlock can't be relocked. Thus their only options are to escape or survive until the time limit is reached. The taggers are given knives and tasked with killing at least one hider, with any who fail to kill a hider within the time limit subject to elimination.
• Kick the Dog: 
  • Jeong-dae and Seon-nyeon rub the salt in Gi-hun's wounds with the former "thanking" him for eliminating majority of Xs, allowing the games to continue.
  • Nam-gyu taunts Min-su over Se-mi’s murder.
• Mercy Lead: Hide-and-seek, just like its namesake, gives the hiders a few minutes to spread out through the maze before allowing the taggers to pursue them, as obviously the hiders would be slaughtered if the staff released both sets at once.
• Nice Job Breaking It, Hero!: As Player 100 ruthlessly brings up, all Gi-Hun's rebellion did was kill a majority of Xs that could have voted to end the games. Now the Os, at least for now, have an unbeatable majority.
• Properly Paranoid: Woo-seok correctly suspects that Captain Park may have had a hand in the drone pilot's death, and chooses to stay behind the next day to confirm his suspicions. He warns Jun-ho not to trust Park, both the day before and as they are departing in the morning.
• Red Is Violent: Invoked together with Blue Is Calm. The team that is tasked to hunt down and kill the hiders is the Red Team, and each team member is given a knife to do so.
• The Reveal: Gyeong-seok (Player 246) turns out to still be alive; he was non-fatally shot by No-eul and was brought to the operating room so she could save him later.
• Your Approval Fills Me with Shame: Player 100 remarks that Gi-Hun's attempted rebellion wound up killing a lot of the X's, ensuring that the O's would win the vote. He even encapsulates this by not only speculating that this was a plan to get a larger cut of the profits but also getting his crew to applaud for him.