Japan’s government is preparing to issue fresh debt as part of a supplementary budget aimed at shielding households from soaring energy costs linked to the ongoing Middle East conflict, a move that is rapidly intensifying concerns across global bond markets. Investors are increasingly worried that additional fiscal stimulus, combined with persistent inflation and delayed monetary tightening from the Bank of Japan, could further destabilize Japan’s already fragile financial position.

Bond Markets React Sharply to Japan’s Fiscal Shift

Financial markets responded aggressively after reports emerged that Prime Minister Sanae Takaichi had instructed officials to begin drafting a supplementary budget, reversing her previous stance against additional spending measures.

The announcement immediately triggered renewed selling pressure across Japanese government bonds. The benchmark 10-year Japanese government bond yield climbed to 2.8% on Monday, marking its highest level since 1996, while the 30-year yield reached a record high.

Investors fear that increased debt issuance could significantly worsen Japan’s already massive public debt burden, which remains among the highest in the developed world relative to gross domestic product.

The extra budget is expected to focus heavily on subsidies designed to offset rising gasoline and utility bills after the war-related surge in oil prices sharply increased import costs for the energy-dependent Japanese economy.

Market strategists say the government’s sudden shift toward additional fiscal expansion has intensified fears that policymakers may prioritize short-term economic support at the expense of long-term financial stability.

Analysts at Sumitomo Mitsui Trust Asset Management noted that markets are already beginning to price in the possibility of an extra budget ranging between 5 trillion yen and 10 trillion yen, substantially larger than some earlier expectations.

Inflation and Weak Yen Create Pressure on the BOJ

The fiscal expansion debate comes at a particularly difficult moment for the Bank of Japan, which is already facing mounting pressure to accelerate interest rate hikes.

Japan’s wholesale inflation climbed to 4.9% in April, the highest level in three years, driven by rising energy prices and a weaker yen that continues increasing the cost of imports.

The Japanese currency weakened further to nearly 159 yen per dollar on Monday, its softest level since late April, amplifying concerns about imported inflation and declining consumer purchasing power.

Markets now estimate roughly a 70% probability that the Bank of Japan will raise its short-term policy rate from 0.75% to 1.0% at its June meeting. Several policymakers have recently signaled growing concern that the central bank risks falling behind the curve in controlling inflation.

However, the sharp volatility in bond markets complicates the BOJ’s decision-making process. Central banks often avoid tightening policy during periods of severe market stress, yet delaying rate hikes could further weaken the yen and intensify inflationary pressures.

Nomura Securities strategist Mari Iwashita warned that if inflation risks continue escalating, the BOJ may ultimately need to raise rates as high as 1.5% by the end of the current fiscal year, a dramatic shift for a country that maintained ultra-loose monetary policy for decades.

Markets Fear a Broader Confidence Problem

Beyond the immediate bond market reaction, investors are becoming increasingly concerned that Japan may be entering a dangerous combination of weak growth, rising inflation, fiscal expansion, and monetary tightening.

Some strategists warn that this environment could trigger simultaneous selling pressure across bonds, equities, and the currency market — a pattern sometimes associated with weakening investor confidence in broader economic management.

Japan’s Nikkei index declined Monday as markets assessed the possibility that rising borrowing costs could eventually pressure corporate profits and consumer spending. At the same time, higher long-term yields threaten to increase debt servicing costs for the government itself.

Looking ahead, investors will closely monitor the final size of the supplementary budget, the BOJ’s June policy decision, and developments in global energy markets. If oil prices remain elevated and inflation continues accelerating, Japan may soon face one of its most difficult economic balancing acts in decades.