Armored Core: Tower City Blade

Following the dissolution of the Corporations from countless conflicts, independent nations have taken over, claiming territories to become their own countries. In the battle for land and resources, independent mercenaries known as Ravens piloting powerful, customizable machines known as Armored Cores are hired to wage these battles. Unrelated to these warring factions is another place where Ravens may fight and compete each other, known as the Arena. Here, skilled pilots test their mettle against one another to become the top-ranked pilot.

(Source: Armored Core Wiki)