The catastrophe in Japan has placed renewed focus on the country’s already fragile economy—and brought unexpected profits to investors who have long bet that the nation eventually will be dragged down by its debt problems.

In recent years, a chorus of voices has warned that Japan is facing an inevitable crisis to be brought on by a stagnant economy, a shrinking population and the worst debt profile of any major industrialized country.

Hedge-fund managers from Kyle Bass of Hayman Advisors LP in Dallas to smaller firms like Commonwealth Opportunity Capital have made money since the earthquake on long-held bets on Japan’s government and corporate bonds.

Though the economic toll of the earthquake is far from clear, the immediate response in the financial markets has been a decline in stock prices, with the Nikkei Stock Average down 7.8% in two days (including Friday, when the quake hit near the end of the trading day). The price for insuring against a default by Japan on its government debt, a popular way to position for a financial crisis in Japan, has jumped. But in a move that runs counter to the expectations of some long-term Japan bears, the yen has strengthened on expectations that Japanese investors and corporations will be buying yen as they bring money home in coming weeks and months.

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