Actually, it’s the western region of Japan that uses 60 Hz. In the early days of electrification (around the 1880s), during the transition from DC to AC, western Japan adopted a 60 Hz standard using a generator built by General Electric. Meanwhile, eastern Japan imported a generator from the German company AEG, which operated at 50 Hz.

That area of Japan's standard is actually 100 volts/60 Hz from what I recall. Which is even weirder