Eager to know why her best friend’s boyfriend dumped her for a man, the headstrong Eiya Arakawa suggests a meeting with them. Gathered together at a café, Yuuga Oota agrees to answer Eiya’s questions only if she can correctly ascertain the relationship of a couple sitting across from them, which she does on her first attempt. Amazed by her astounding intellect and intuition, he invites her to a private meeting where he introduces her to the concept of Slave Control Method, or SCM, a retainer-like device that has the ability to turn people into slaves. When two SCM users enter a duel, the devices exert a powerful influence on their brains. Once the duel is over, the SCM amplifies the loser’s sense of obligation and forces them to bend to the will of the winner. Wanting desperately to test his own abilities, Yuuga asks Eiya to act as his insurance in the event that he himself becomes a slave. Granted access to 10 million yen, Eiya’s job is to convince Yuuga’s would-be master to free him from his servitude. Though hesitant at first, Yuuga’s words resonate with her personal yearning for something more from her life, and she agrees to his request. However, when a mysterious organization begins rapidly accruing slaves, Eiya becomes entangled in a game far more dangerous than she ever could have imagined.

It can be rough transferring to a new school—even more so if you don't want to make any friends, like Nobuaki Kanazawa. But the reason for his antisocial behavior soon becomes clear when his class receives a text from someone called "The King." Included are instructions for the "King's Game," and all class members must participate. Those who refuse to play, quit halfway, or don't follow an order in the allotted time of 24 hours will receive a deadly punishment. Having played the game before and watched as those around him died, Nobuaki tries to warn his clueless classmates. Unfortunately, they only believe him after the King's Game claims its first casualties. Stuck in a horrific situation with no chance of escape, Nobuaki has a choice: put his own survival above those around him, or do what he couldn't before and save his classmates.