Take a look at Reigen Fujii demonstrating his four-string shamisen on NHK! Note that it’s an electric shamisen, which is what gives it a warmer tone. 
四味線！That’s really cool!
Awesome cover. NHK Blends produces some amazing quality performances and pulls from an impressively diverse library of songs.
What’s the tuning on a four string shamisen? I’d love to hear the story behind it. Can’t imagine they’re very common.
Nice. One of my favourite songs too Interesting to see a Shamisen with geared guitar tuners as opposed to the “traditional” ones that slip all the time 
Joel, I am curious about it too! Knowing Reigen loves sansagari, I would guess it is close from that with the biggest string lower like Dropped D on a guitar or something like that.
But maybe I am totally wrong about it so I hope Kyle or Reigen or Kevin jumps in to enlight us!
4-strings shamisen? Wow!
So, no one knows about the tuning yet?