https://en.wikipedia.org/wiki/School_uniforms_in_Japan

The sailor fuku (セーラー服, sērā fuku) (lit. 'sailor outfit') is a common style of uniform worn by female middle school students, traditionally by high school students, and occasionally, elementary school students. It was introduced as a school uniform in 1920 at Heian Jogakuin (平安女学院)[9] and 1921 by the principal of Fukuoka Jo Gakuin University (福岡女学院),[10] Elizabeth Lee. It was modeled after the uniform used by the British Royal Navy at the time, which Lee had experienced as an exchange student in the United Kingdom.