This is an ensemble
using three Japanese instruments to play a traditional piece of Japanese
It is usually the case that the instruments used are the koto, the shamisen and shakuhachi. The use of these three allows for variation in the sounds and tones that are produced. Though three different instruments are used, the number of instrumentalists is not set. It can be as few as one per instrument, or as many as three or even more.
A classical example of a piece with one instrumentalist per instrument, is Shin Musume Dojoji, a wonderful sankyoku based on an ancient fairy tale.