Difficult to say as this set didn't have the booklet. My very sketchy understanding is that Yonin No Kai were an ensemble aiming to re-present, and possibly reinvigorate, traditional Japanese music,they formed in the 50s.
Shakuhachi, koto, sangen and jushichigen are featured instruments, sometimes with chamber orchestra added playing pieces by a variety of composers and some traditional pieces. I don't know if the composers were contemporary in the 70s when the box was released or were earlier. I need to do that research still.
I've often flirted with Japanese music, primarily through shakuhachi playing (sadly not by me I hasten to add) and love the sound so dived in when Clifford suggested this set.
Clifford may well know more and will hopefully be able to correct any misunderstandings I'm listening under.