You can defend the exchange rate, or set your own interest rates, or let capital move freely. Pick two. Every failed currency defence is a country discovering it tried for three.
In April and May of 2024, Japan's Ministry of Finance spent about ¥9.8 trillion — roughly $62 billion — buying yen. The dollar dropped about five yen in minutes, then drifted back toward where it started within weeks. That is the normal outcome, and the reason is structural: defending a falling currency and capping a rising one are not the same trade.
— Educational, not financial advice.