Eia Arakawa, a sharp twenty-year-old, is pulled into the SCM game by Yuuga Ohta, a restless newcomer who collects slaves to kill his boredom. The SCM is a tiny device worn behind the teeth: two people who both carry one can stake their freedom on a duel, and the loser becomes the winner's slave, body and will. As Eia investigates how the SCM spread and what binds the people caught in it, the duels around her grow stranger and more dangerous.