The Japanese yen is strong relative to other currencies like the US dollar for several reasons. Japanese domestic interest rates are lower than other countries, leading to demand for yen. Japan also has an aging population that saves more. Additionally, Japan runs a large trade surplus by exporting more than it imports, increasing demand for its currency. This trade surplus, along with Japanese investment abroad, contributes to the yen being a currency that is in higher demand than supply, making it stronger over time.