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.

Responsible for the theft of the class funds, the application to play Tomodachi Game, and the exposure of all kinds of dirty secrets in Bad-Mouth Sugoroku, Tenji now tries to alienate Shiho from the others so he can have her all to himself. As a result of his attempts, a rift develops between Shiho and Yutori that threatens to destroy their friendship. But while Tenji is busy sweet-talking Shiho and planning his next move, a "special chance" appears for Shiho that might change the direction of the game.

Yuichi and friends reach the end of Kokkuri-san, uncovering dimensions of trickery in the Tomodachi Game that they hadn't imagined. When they move on to a second game, a socially destructive version of sugoroku, the group struggles to maintain balance as personal secrets are revealed and trust is stretched to its absolute limit.

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.

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.

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.

The third game, Friendly Hide-and-Seek, begins. Rival Group K, bolstered by an apparent 'genius' strategist, proceeds with a clear numerical advantage. Eager to regain Yuichi's trust, Tenji volunteers to be Group C's hider, but the couple's plans are strained by the addition of a new female teammate, Mizuse Maria. Yuichi confidently tells Tenji to "just trust me and wait," but then doesn't return for days...

Yuuichi goes to help Kokorogi knowing it will be very dangerous, but things could turn out worse than imagined.

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.

With "true genius" Kei controlling things from the shadows, Group K succeeds in finding Tenji. Facing the "worst thing that could have happened," Tenji makes a phone call to a certain individual. The third game, Friendly Hide-and-Seek, then reaches its conclusion. While the two groups struggled to outwit each other, Shiho, Shibe, and Yutori, who had been temporarily released for the third game, returned to school only to be met with cold stares from their classmates.

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.