Japanese investors, the biggest foreign holders of U.S. debt, are starting to pull money back home as rising Japanese government bond yields make domestic debt look better than Treasuries. That shift is showing up just as the Treasury Department sold $25 billion of 30-year bonds at a 5% yield for the first time since 2007, a sign that the world’s deepest bond market is facing a harder sell.

For years, Japanese savers had little reason to stay in their own market. The Bank of Japan kept rates near zero and, for a long stretch, even below zero to fight deflation in a stagnant economy. That changed in 2024, when the central bank tightened four times. Yields on 10- and 30-year Japanese government bonds have since jumped to their highest levels since the 1990s, and investors now widely expect another move next month that would lift the policy rate from 0.75% to 1%.

Mark Dowding, chief investment officer at BlueBay, said the change in incentives is starting to redirect capital in a way global markets will feel. “The new money that's being put to work won't be put to work overseas. It won't be going into U.S. corporate bonds. It won't be going into U.S. Treasuries. It will be going into those domestic allocations,” he said.

The pressure is not coming from one source. Hotter inflation has helped push Japanese yields higher, while the Bank of Japan is expected to tighten for the fifth time since 2024 as the Iran war sends oil prices higher. Prime Minister Sanae Takaichi is also seen boosting government spending to revive growth and blunt the oil shock, a mix that could keep domestic borrowing needs elevated and keep attention fixed on local rates rather than foreign ones.

That shift matters today because it lands at a moment when the U.S. Treasury market already looks fragile. In mid-February, a Treasury offering drew the highest demand ever in the history of 30-year auctions, but March brought weak demand for two-, five- and seven-year notes. At the same time, foreign central banks have stepped back from the U.S. bond market and hedge funds have taken on a bigger role as buyers, while a flood of corporate debt competes with government borrowing for investors’ cash.

Matt Smith, chief investment officer at Ruffer, said the domestic pull is building and could eventually spill into the currency. “Pressure is building — long-end domestic yields are rising,” he said. “And the institutional framework is now ‘please can you bring this money home’. We think yen strength will happen slowly, then quickly.”

The money is already moving. March saw the largest monthly inflow ever into Japanese sovereign bond funds, and BlueBay launched its first Japanese bond fund that same month. The Federal Reserve’s next move is still expected to be a rate cut, but that timing may now slip back into 2027, which leaves U.S. yields vulnerable if Japanese buyers keep finding better returns at home.

The question for investors is no longer whether Japan can hold capital in place. It is how much of that estimated $1 trillion in Japanese Treasury holdings gets redeployed as domestic yields keep climbing and the gap between Tokyo and Washington narrows. If the shift accelerates, the change will be felt first in auction demand, then in pricing, and finally in the cost of financing the U.S. government itself.