Nao Kanzaki is a university student whose excessive honesty and naivete are her defining, and almost debilitating, traits. One day, she receives a mysterious package containing 100 million yen and a notice that she has been selected as a contestant in the Liar Game Tournament. The rules are brutally simple: players must try to swindle their opponent out of their 100 million yen within a set time period. The winner keeps their prize money, while the loser is saddled with a debt of 100 million yen to the tournament organizers, to be collected by any means necessary.

Nao's initial relief at discovering her opponent is her trusted former junior high school teacher, Kazuo Fujisawa, quickly turns to despair. The once-kind teacher, hardened by personal misfortunes, easily tricks the trusting Nao and steals her entire sum. Desperate and facing financial ruin, Nao turns to the police for help, but they are powerless. However, a detective suggests she seek out a certain genius: Shinichi Akiyama.

Akiyama is a brilliant criminal psychologist and a legendary swindler who has just been released from prison. He was incarcerated for single-handedly bankrupting a massive, fraudulent multi-level marketing company—the same company that had swindled his own mother, driving her to suicide. Initially reluctant, Akiyama is moved by Nao's desperate plea and agrees to help her win the game and clear her debt.

Together, this unlikely pair forms the core of the series. Akiyama is cold, calculating, and a master of psychological manipulation and logical strategy, while Nao is emotionally intelligent, earnest, and trusts in the fundamental goodness of people. He uses her honesty as an unexpected weapon, a tool to build trust and uncover the truth where deception reigns. Their goal evolves from simply winning to freeing not only themselves but also other contestants from the clutches of the game.

After defeating Fujisawa in the first round, Nao and Akiyama are forced to advance to the next stage. The second round, titled Minority Rule, introduces a larger cast of players. The premise is that a group of 22 contestants must answer a Yes/No question. The majority vote is eliminated and incurs a massive fine, while the minority advances. This process continues until a single winner claims a jackpot of over 2 billion yen.

This round introduces a key recurring character, Yuji Fukunaga, a sly and calculating manipulator who initially appears as a woman named "Hitomi" to deceive the other players. The contest becomes a chaotic battle of shifting alliances, betrayal, and mind games, with Akiyama meticulously planning to ensure he and Nao can survive and use the winnings to pay off the debts of their eliminated rivals. His ultimate goal, however, is not the money, but to expose the shadowy organization running the tournament.

The series takes place within a closed-world setting—isolated rooms, game arenas, and neutral meeting places controlled by the LGT (Liar Game Tournament) Office. This office is populated by masked dealers, a coordinator named Eri, and the enigmatic voice of the main dealer, Solario. The omnipresent and almost supernatural control the organization exerts over the game reinforces the sense of a rigged, inescapable system.

As the rounds progress, Nao and Akiyama face increasingly formidable antagonists. The most significant is Norihiko Yokoya, a wealthy, cold, and eerily calm young man who treats the game as a military dictatorship, buying loyalty and commanding his pawns with an iron fist. Yokoya becomes Akiyama's greatest rival, a dark mirror who uses his intellect and resources not for escape, but for absolute domination. The conflict between Akiyama's desire to dismantle the game from within and Yokoya's obsession with winning at all costs drives much of the later narrative tension. The series follows their journey through multiple psychological battles, from the Restructuring Game to the Smuggling Game, as they struggle to survive, protect their allies, and uncover the true purpose of the Liar Game.