Kai Ichihara is a high school student who gets a weird email asking if he wants to try "Slave Go," a mobile game that enslaves specific people if they are "captured" by taking their picture. After using the app on two people, Kai is shocked to discover they have vanished, meaning the game he assumed was just a joke is actually real. Then, when his good friend Rinna Date also disappears, he worries she has suffered the same fate. Confronted by a mysterious man named William Gotou, Kai is taken to a room where the slaves he captured are forced to participate in a death battle devised by wealthy members of "Society," an exclusive, underground community. Betting is conducted using a currency called Delos, and if someone loses all their money, they become a slave. Although he manages to win his first game, this is only the start, as Kai learns that Rinna has indeed become a slave, and to free her, he must pay a fee of one hundred million Delos. With William serving as his guide, Kai strives to capture powerful slaves to help him liberate Rinna and free both of them from the grip of Society's evil game.