Nao Kanzaki, a college student whose naive and compulsively honest nature often leaves her taken advantage of, arrives home to find a mysterious package. Inside is a suitcase containing one hundred million yen and a letter informing her that she has been selected to participate in the Liar Game Tournament. The rules are deceptively simple: she is paired with an opponent and given thirty days to swindle the other person of their hundred million yen. The winner keeps the full two hundred million yen prize, while the loser is saddled with a one hundred million yen debt to the game's shadowy organizers, collected by any means necessary. When Nao discovers her opponent is Kazuo Fujisawa, a trusted former middle school teacher, she believes the game will be a formality. Her trusting nature proves disastrous, as Fujisawa easily tricks her into handing over her entire stake, leaving her devastated and facing an impossible debt.

With the police unable to intervene in what is considered a private contract dispute, a desperate Nao is directed to Shinichi Akiyama, a brilliant criminal psychology graduate recently released from prison. Akiyama earned his incarceration by single-handedly bankrupting a massive multinational scamming operation that drove his mother to suicide. Initially reluctant, he agrees to help Nao in exchange for half her winnings. Using psychological manipulation and meticulously crafted counter-deceptions, Akiyama masterfully turns the tables on Fujisawa. After winning the first round, Nao cannot bring herself to let her former teacher suffer; she gives him her winnings to pay off his debt, forcing her to continue the tournament to clear her own remaining financial obligation. Akiyama, fascinated by her incorruptible nature and seeing a reflection of his mother, decides to join the game as a full participant, determined to expose the masterminds behind the organization.

The second round introduces a larger-scale game called Minority Rule. Over twenty contestants, each given another hundred million yen, must repeatedly answer yes-no questions. The majority vote in each round is eliminated and incurs a penalty, while the minority advances. This process continues until a single winner claims the accumulated billions. Nao and Akiyama find themselves pitted against a cast of cunning and desperate opponents, including the chameleon-like Yuji Fukunaga, a master of disguise who uses shifting personas and alliances to manipulate other players. Akiyama engineers an elaborate strategy to secure a win, but the game forces him to incur a massive debt himself, locking him into the tournament for the foreseeable future.

As the rounds progress, the games escalate in complexity and cruelty, moving from one-on-one psychological battles to intricate team-based competitions that exploit trust and betrayal. Akiyama and Nao emerge as a formidable duo. He provides the cold, calculating strategic genius, while her sincerity, which initially seemed like a weakness, proves to be an invaluable weapon. Her ability to earn genuine trust allows her to unite opponents who would otherwise be at each other's throats, creating alliances that defy the game's cynical premise. Their journey brings them into conflict with Norihiko Yokoya, a chillingly calm and wealthy rival who treats the game as a dictatorship and sees other contestants as mere pawns to be bought and controlled. Yokoya becomes Akiyama's primary antagonist, matching him in intellect while representing the absolute worst of the game's corrupting influence.

The live-action television series follows the main storyline through the first several rounds of the tournament. The first season concludes with the intense third round, a complex revival game where former losers get a chance to return, culminating in a direct psychological showdown between Akiyama and Yokoya. The story continues in Liar Game Season 2, which introduces even more elaborate scenarios, such as the contagious musical chairs game, pushing the protagonists to their limits. The overarching narrative arc finds Nao and Akiyama consistently refusing to abandon other players to debt, instead devising strategies to save their opponents while still defeating the system. Their ultimate goal shifts from merely surviving to dismantling the Liar Game Tournament from within. This leads directly into the feature film Liar Game: The Final Stage, which resolves the central mystery of the organization's purpose and brings the long-running battle of wits between the honest girl and the genius swindler against their greatest adversaries to a definitive close.