Shamisen is definitely a fast instrument, I was wondering if there any sad slower pieces I could learn
Gion Kouta…thread title in Bachido and download of file via dropbox…
P
Been playing Sakura…
Tosa no Sunayama - 十三の砂山
It’s about the aftermath of a huge tsunami. It can be played either way, just as you like. You can play it straight through, or as some players do, add a lot of dynamics in Speed and Volume to emphasize the changing feelings of tragedy and hope.
I would recommend to you the Bachido-Course of Tosa no Sunayama 
https://bachido.com/school/sunayama
Regards
Andreas
The jiuta genre is full of melancholic pieces, if you can read the music (or find it transcribed).