Which country uses a flag with a red circle on a white background?

Japan

The flag of Japan, known as "Nisshōki" or more commonly "Hinomaru," symbolizes the sun in the form of a red disc. This simplicity reflects Japanese values of simplicity and harmony. The sun plays a central role in Japanese culture, with the country being nicknamed "the land of the rising sun." This flag holds deep significance for the Japanese people, evoking nature and spirituality.