Doomsday World: Gladiator

After a thousand years of world war, Earth has become a wasteland, with fewer than 300,000 humans remaining, living in underground cities of the Eastern and Western factions at the North and South Poles. The two factions have been constantly at war to conquer each other and fight for survival resources. Robot warriors, humans, and mutant species battle endlessly for dominance, with no peace in sight. Controlling all of this is the Think Tank created by humans, which has long since escaped human control and become omnipotent. It can support any faction to balance power, aiming to distract all parties and hide its own agenda. The only solution is a key called the 'Cosmic Key Final Sword,' which is composed of several parts, but their locations and holders are unknown. — Description from novelcodex.org