
A Bachigawa is a protection for the skin of the Dou.
A Bachigawa is a protection for the skin of the Dou (the body of the Shamisen), because in the Tusgaru Shamisen Style, it's played very roughly.
Also, when using an artificial skin on the dou, it protects the Bachi (the plectrum) from excessive wear. Because artificial skins tend to be rougher than natural ones.
The Bachigawa are self-adhesive and require no further tools to install.