Nikkei at All-Time High — Why Can't KOSPI Keep Up?

The Nikkei Just Hit an All-Time High

On September 16, 2026, Japan's Nikkei 225 index closed at 63,923 — a record high. This happened even as U.S. markets fell the day before and tensions in the Middle East remained elevated. A wave of bargain buying after a short-term dip drove the rebound. Meanwhile, South Korea's KOSPI failed to follow suit. Why?

Why the Nikkei Is Strong — Reason 1: Weak Yen

The first reason Japan's market is strong is the weak yen. When the yen loses value, Japanese exporters benefit. For example, when Toyota sells cars in the U.S. and earns dollars, converting those dollars back to yen yields more money when the yen is weak. So as the yen weakens, the earnings of major exporters like Toyota, Sony, and Canon improve — and their stock prices rise with them.

Why the Nikkei Is Strong — Reason 2: Bank of Japan Policy

The Bank of Japan (BOJ) kept interest rates near 0% for a long time — even as other countries hiked aggressively. That cheap money flowed into stocks, helping push the Nikkei higher. The BOJ has recently started nudging rates up slightly, but they remain far lower than most other major economies.

Why Does KOSPI Move Differently?

South Korea's KOSPI is heavily weighted toward semiconductors (Samsung Electronics, SK Hynix) and export stocks — but it doesn't get the same weak-currency boost Japan does. The Korean won has held relatively firm against the dollar, so exporters don't get the same earnings tailwind. On top of that, Korea's higher interest rates make bank deposits more attractive than stocks for many savers.

A Quick Comparison: Nikkei vs. KOSPI

The Nikkei's record highs come from a unique combination: export-heavy index + weak yen + ultra-low rates. KOSPI is more sensitive to the semiconductor cycle, foreign investor flows, and the won-dollar rate. They may both be "Asian markets," but they operate on very different logic. That's why the Nikkei can surge while KOSPI stays flat — and vice versa.

What Is 'Bargain Buying'?

Another reason the Nikkei rebounded today is bargain buying. It refers to the act of purchasing stocks after a sharp short-term drop — based on the judgment that prices have fallen enough to be attractive. Markets always have investors waiting on the sidelines for the right moment. When prices drop sharply, they rush in all at once, triggering a rebound.