This is a prequel to the original Slave Zero, released in 1999. The game's events take place five years before the events shown in the first part. Megacity S1-9 is ruled by the great Khan, who terrorizes the population with his controlled living machines. A group of rebels wants to end the tyranny and uses the enemy's weapon against him. The warriors capture one of the biomechs and turn it to their side.
The game features boss battles, a special training mode, and endgame content — the procedural tower "Castelo-Vermelho," where players can compete for leadership on the online leaderboard.