Muramasa is the name of a smith school known for making blades that were said to be cursed with bloodlust. 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 wield blades made by Muramasa. This contributed even more to the Muramasa legend and led to many plays and dramas in Japanese literature featuring the blades. Due to the stigma attached to them, many Muramasa blades had their signature changed or removed. Since opponents of the Tokugawa Shoguns would often wish to acquire Muramasa blades, forgeries of Muramasa blades were also often made. Ironically, the only Muramasa blade that ever helped the Tokugawa was Tonbogiri, the spear of Honda Tadakatsu.
It has also been told that once drawn, a Muramasa blade has to draw blood before it can be returned to its scabbard, even to the point of forcing its wielder to wound himself or commit suicide. Thus, it is thought of as a demonic cursed blade that creates bloodlust in those who wield it.
The artwork also features a Kappa and Chochin Obake. A kappa is a yōkai demon or imp found in traditional Japanese folklore. In Shintō they are considered to be one of many suijin, their yorishiro, or one of their temporary appearances. Kappa are distinguished for having a small pool of water suspended on top of their head, signifying their life force and habitat.
See Aka "Red" Chochin for Chochin Obake