After the hard-earned funds for their expensive high school class trip are stolen, sophomore Yuichi and his four best friends are kidnapped by Manabu, a surreal character from a creepy late-night anime show. The mischievous Manabu challenges the students to a series of mind games that the five must decipher and outwit in order to win back their trip funds, uncover the thief, and pay off a huge and mysterious debt.

Dark secrets are exposed as the second game, Bad-Mouth Sugoroku, continues. Yutori is devastated when a traumatic episode from her past is revealed, leading her to suspect the only other person who knew—Shiho. As debts increase, the five friends are driven further apart. With no one else to turn to, Yutori clings to Yuichi for help, and Yuichi pledges his support.

Shibe reels from the accusation that he has "actually killed a person." Despite protesting that he never did such a thing, he loses the audience's confidence and is thrust into first place. Meanwhile, Tenji finds himself in a distressing situation after realizing Yuichi is the one who wrote the card. Yuichi then makes the shocking announcement that he knows who the traitor is.

Backed into a corner by Yuichi's plan, Tenji is forced to confess that he applied to play Tomodachi Game. Yuichi spells out the traps he set to smoke out the traitor and reveals that he had been manipulating the game from the start. The second game then reaches a breathtakingly unexpected conclusion.

After clearing Bad-Mouth Sugoroku, Yuichi and Tenji find themselves trapped in a dark cave for three days. During their isolation, Tenji makes the shocking revelation that he had already experienced a Tomodachi Game in the past. Meanwhile, a team of new opponents lies in wait outside, anxious to challenge the two partners to a grueling third game.

Yuichi, who hasn’t left the starting point in the two days since the game began, suddenly announces his desire to switch to Group K. The Group K members, puzzled by Yuichi’s apparent intention to abandon his hiding teammate, ask their Captain to decide whether or not to let Yuichi in. Meanwhile, Tenji, who has stayed in hiding and trusted Yuichi all along, is finally reaching his physical breaking point.

Finally able to shake his Group K guards, Yuichi succeeds in delivering food to Tenji. After being pushed off the cliff by Yuichi, Maria slowly gets closer to her saviors Hyakutaro and Chisato, but that too is a trap set by Yuichi to destroy the friendships in Group K.