History turns on the smallest of things, and the Battle of Sekigahara was no small thing. A few traitors instead remain loyal, a few brave men instead cower, and Tokugawa Ieyasu never becomes Shogun. No isolationism, no end to ties with Portugal, and the Edo Period becomes Japan's Colonial Period.
433 years and a three-way Cold War later, the Monarchist bloc has stepped forward with a treaty proposing an alternative to conventional (or nuclear) warfare for international conflict resolution. The Treaty of Budapest requires signatories to stake their interests on single combat between their Duelist mechs.
The ink on the treaty is barely dry, and already the People's Republics of Gran Colombia has contested the California Shogunate's control of Mexico City. Now Chris Hernandez, samurai and fighter pilot, must wield California's Duelist against the forces that seek to turn La Ciudad's twenty million souls into the forced labor that turns the wheels of the Red war machine.