In the apocalyptic chaos of Fortress Doomsday, protagonist Gage Thorne is reborn with a unique "Rage System"—fueled by vengeance and emotional energy. As mutated beasts, ruthless gangs, and the mysterious Esper Alliance rise, he transforms his humble shelter into an impenetrable stronghold. From Tier-E defenses to nano-enhanced gear, Gage battles Alpha Zombies, Espers, and his own past to uncover the truth behind the Starlight Project and the ABRI conspiracy. Survival is just the beginning—domination is the goal.