I once met someone who made a homemade case for her ukulele. Does anyone know of a way to make a homemade case for a shamisen?
I know must be a stupid observation. If you want to build a case… just buy materials, and maybe see photos
I think you can easily build a hardcase for your shamisen out of wood and styrofoam. Start out with measuring the instrument, 400 cm width, 20-25cm height and 140cm length might be enough (measured by a tsugaru shamisen) which still might by a bit too bulky.
Then add a small layer styrofoam to the backs of each halfs and cut a precise outline of the instrument into another thicker layer.
Glue fleece or satin to it and voila: Hardcase.
Of course it all sounds easier than it is in the theory but with a little woodworking experience you should be able to do this.