Europe is struggling with its sovereign debt crisis, and government and the central bank in each European country implemented large-scale measures to support their fi nancial markets after the fi nancial crisis. What happens when we attempt a cold shutdown of one of the biggest debt spirals that the world has ever seen? I analyzed the mechanism of the sovereign debt crisis using a two- player model with game theory and real options. The study found that the market and nations working together unconsciously (implicit alliances) has brought about the stability of fi nancial systems. These implicit alliances postpone a fi nancial system breakdown because supporting organizations and nations expect a restorative possibility, and continue fi nancial assistance. But it also found problems associated with the "concentration of the exposure to supporting nations".