I consider the Shamisen the "king" of Japanese instruments in the same way that the violin is the "king" of european music. It's everywhere, folk music, classical art music, Kabuki, and recently shows up in pop every now and then.
I'm a shakuhachi player and play mostly traditional Sankyoku music. "Three voices", the traditional ensemble is Shamisen, Koto - a 13 string zither, and Shakuhachi, a bamboo flute. It's a great joy to study with and play with the string players.