Shinichi Akiyama is a central figure in Liar Game, known for his exceptional intelligence and a past marked by tragedy and revenge. He is a former graduate student who became a legendary con artist after a devastating personal loss. His motivation stems from the suicide of his mother, who was driven into insurmountable debt by a multi-level marketing scam and took her own life so her life insurance could pay for his education. Consumed by a need for retribution, Akiyama used his intellect to single-handedly swindle that same company into bankruptcy, an act that led to his imprisonment for fraud. Upon his release, he is immediately approached by a young woman named Nao Kanzaki, whose desperate plea for help and unwavering, naive honesty remind him painfully of his own mother.

Personality-wise, Akiyama is calm, logical, and deeply cynical. He is a master of psychological insight, able to read people's intentions and manipulate situations with surgical precision. His default mode is one of skepticism; he believes that doubting others is not an act of cruelty but an effort to truly understand them, arguing that indifference is far more harmful than suspicion. Despite this cold exterior and a pessimistic view of human nature, he possesses a strong, albeit buried, sense of justice and compassion. He is not ruthless for the sake of winning and is often troubled by his own manipulative abilities, seeing uncomfortable similarities between himself and his more malevolent rivals. His interactions with Nao slowly reveal a warmer, more protective side, though he remains reserved and uncomfortable with overt emotional displays.

Akiyama's primary role in the story is that of a strategist and a guardian. He initially agrees to help Nao win the Liar Game for a fee, but his motivation quickly evolves. While he supports Nao's idealistic goal of saving every player from debt, his personal objective is far more pointed: to expose and destroy the organization behind the Liar Game, which he sees as a vile institution that preys on human weakness. He participates in the game as a substitute for another player and rapidly becomes an unofficial leader, using his genius to devise intricate plans that consistently outmaneuver opponents.

The most significant relationship in his life is with Nao Kanzaki. Their bond is symbiotic and complex. She serves as his moral compass and emotional anchor, pulling him back from his darkest, most cynical impulses. Her ability to trust and appeal to the goodness in others becomes a powerful tool in his strategic arsenal, something he can never replicate himself. In turn, he is fiercely protective of her, constantly trying to pay off her debt and remove her from harm's way. Through Nao, Akiyama begins to heal, learning that vulnerability and trust are not merely weaknesses. He also shares a tense rivalry with Norihiko Yokoya, the man behind the scam that ruined his mother, viewing him as a dark mirror of his own capabilities. His relationship with other allies, such as Yuji Fukunaga, is based on mutual respect and strategic necessity, though he remains perpetually wary of betrayal.

Throughout the series, Akiyama undergoes significant development. He starts as a solitary, revenge-driven figure who uses people as pieces on a board. Under Nao's influence, he gradually becomes more willing to trust his allies and accept strategies that do not rely solely on his control. A pivotal moment comes when he refrains from completely destroying Yokoya, choosing mercy at Nao's behest, a decision that would have been unthinkable for him earlier. His arc is one of redemption, moving from a man defined by past trauma and guilt to one who finds a new purpose in protecting others and dismantling a corrupt system, all while learning to reconnect with his own humanity.

His abilities are his defining trait. He holds a master's degree in psychology, which gives him a theoretical foundation for his exceptional skills. More than that, he is a genius-level analytical thinker capable of processing complex game rules, calculating probabilities, and predicting the behavior of numerous players with superhuman speed. He excels at finding loopholes in rules and thinking outside the box to create unorthodox winning strategies. He is also a master of disguise and deception, skills he uses to trick opponents and gather information. His greatest strength, however, is his ability to remain calm under pressure, turning even the most dire situations to his advantage through sheer force of intellect.