Yuuichi Katagiri, Yutori Kokorogi, Tenji Mikasa, Shiho Sawaragi, Makoto Shibe and you, all school friends, even though you and Katagiri had known each other since childhood and were like inseparable and equally sadistic lovebirds, all your friends were mired in debt. That's how it started. You have all been greeted by a cartoon-like figure named Manabu, who is cosplaying a children's show character known for stealing from his friends. Manabu explains that you all have 20 million debts in your head. If they decide to leave, the debt will not be paid off. The best choice to make is to play a game called "Tomodachi Game" to pay off your debts.

Manabu advises Yuuichi and the others to participate in the Adults' Tomodachi Game, where the money won is very high, but there are also great risks as the game is played by adults. As the games become increasingly serious, however, Yuuichi begins to show a much more sinister side. He shows little remorse for any of his more devious actions and appears sadistic at points where he takes pleasure in the misfortunes of his enemies. He does not hesitate to use any specific means to achieve his goals, such as threatening to assassinate Kaidou or using Kokorogi to blackmail a teacher.

Shibe: "At least we're getting past the games. It's getting harder, shit."

Kokorogi: "Katagiri-kun is getting impossible! He pushed me onto that teacher like I was just bait!"

Mikasa: "He's doing what's best for us, stop being a crybaby girl, Kokogori."

Sawagari: "Indeed, but I wonder when it will end, the difficulty is increasing."

Katagiri: "Ouch! Ouch! Silence all of you. We're going to win this shit by hook or by crook, but stop acting like chickens."