Japan's largest life insurers are carrying huge paper losses on their bond holdings, a warning sign for the country's financial system.

• Japan's fourth-largest life insurers are sitting on about $96 billion in unrealized losses on Japanese government bonds.
• The losses come from rising bond yields, which push down the value of the older, lower-rate bonds these insurers already own.
• For now these are only paper losses, since insurers can hold the bonds until they mature.
• The danger is a cash crunch: if customers pull money out, insurers could be forced to sell at a loss, turning paper losses into real ones.
• The setup echoes AIG in the 2008 crisis, when an insurer's bad bets forced a government bailout.

Outlook: If Japanese bond yields keep climbing and insurers are pushed to dump bonds, the country's bond market could face serious stress.