Detective Toshiro Niide is a straightforward man with a strong sense of justice. To arrest a criminal, he disregards danger and sometimes acts in ways that seem reckless. Whenever he is on the verge of being consumed by anger, he is guided by the words of his wife, Saori: "Show me kindness rather than anger. That is the right thing for you to do." Niide and six others whose loved ones have been taken, each receive a mysterious message on their phones: "You have been entered in the kiDnap GAME."

The game has finally begun. Toshiro Niide receives his mission: "Apprehend the mastermind behind the kidnappings." Determined to save Saori, Niide pursues the case on his own. Evading the Special Investigation Team (SIT), which has placed him under surveillance as a suspect, he gathers information from Sonomi Uemura, the owner of the food truck Saori frequents, and news reporter Akina Isobe. Yet the kidnappers' motives and objectives remain elusive.

With help from Akina Isobe, Toshiro Niide continues investigating the game's participants across Asia while evading the Special Investigation Team (SIT). He reaches out to them through social media, seeking their cooperation in solving the case. But the rules are clear: "Only one will survive." Determined to save their loved ones, the other participants ignore his appeal.

Only seven days remain in the game. Surgeon Han Kiju struggles with his mission: “Kill someone.” As a doctor, he encounters countless opportunities to take a life. Yet it is precisely because he is a doctor that he cannot bring himself to do so. With concern for his beloved daughter weighing heavily on his mind, Kiju is pushed ever closer to breaking point.