The 80-string koto (or hachijugen) was an invention of Japanese composer Michio Miyagi which appeared In 1923. He added 67 strings to the traditional 13 string koto design, creating an instrument much like a western harp. [1]
References
^Jinko, Katsamura (1986). "Some Innovations in Musical Instruments in Japan during the 1920s" (Print). Yearbook for Traditional Music (International Council For Traditional Music) 18: 157–172.