Quantum Theory is a PlayStation 3 action-adventure game from Koei Tecmo. It follows Syd, a lone warrior fighting through a dark, monstrous tower in a wasted world.

• Cleaned, tested, and guaranteed to play. The disc play surface is in nice condition.
• Original online services for this game or platform have been discontinued; any offline or local modes still work normally.
• Third-person action gameplay centers on battles inside hostile environments that change shape during combat.
• Two-character combo actions pair Syd with a partner character for coordinated attacks.
• The setting focuses on a massive living tower and a ruined world overrun by monstrous threats.
• Trophy support is included for PlayStation 3 progression tracking.

Developed by Team Tachyon, Quantum Theory blends cover-based shooting and sci-fi horror imagery with a tower-climbing campaign structure.