The koto is the national instrument of Japan. It was imported into Japan from China around the 8th century. Since then, the koto has been used in all kinds of music including court music, folk tunes, and even pop music as an accompaniment for a singer.
Since the koto is a zither, it is able to be tuned into different systems. Unlike the other traditional wind instruments, the koto isn't locked down into a single modality. So during the Meiji Restoration, when Japan we becoming Westernized, the kotos could adopt a new tuning system and the other traditional instruments couldn't. This means that the koto became more popular, as it could be used in a non-traditional setting.
With the rise in popularity of Western music, the koto itself also increased in popularity. Schoolchildren began to learn the koto, and played mostly Western tunes. But even with this rise in popularity of Western modality on the koto, the repertory from Tokugawa era remained most popular (Gordon, 109).