Shirasaya is a plain wooden Japanese blade mount consisting of a saya (scabbard) and tsuka (hilt), used when a blade was not expected to see use for some time and needed to be stored.
The Muramasa school of sword-making at Ise province was famous for the extraordinary sharpness of their blades. The earliest known work is dated at 1501.
It is said that the swordsmith Senzo Muramasa, although brilliant, was also insane. Muramasa fell out of favor with the Japanese government when Tokugawa Ieyasu became shogun, establishing the Tokugawa Shogunate, in 1603. It is said that Ieyasu had lost many friends and relatives to Muramasa blades and had cut himself badly with one, so he forbade his samurai to wear the blades. This contributed even more to the Muramasa legend and led to many plays and dramas in Japanese literature featuring the blades.
According to legend, a Muramasa sword could cut a leaf flowing down a stream when held in the stream in the leaf's path. The halves of the leaves were then said to float around the blade as if with a demonic aura. It has also been told that once drawn, a Muramasa blade has to draw blood before it can be returned to its scabbard. Thus, it is thought of as a demonic cursed blade that creates bloodlust in those who wield it.