The Yōtō
A hoplomancer1 like myself has to walk the world to learn about the forgery and smithing of the great masters, perfecting technique and knowledge. During my pilgrimages to discover more about magic weapons I studied at the Muramasa School, an ancient swordsmith academy founded around the 15th century BCE by the legendary Sengo Muramasa. While there, it was obvious that I heard about the most famous creations of master Muramasa: the yōtō.
The literal translation of the name is "bewitching blade", but usually the most accepted versions are "demon blade" and "cursed blade". The weapons had the fame of bringing misfortune to their owners and everyone around them. However, between the hoplomancers, the theory is that every yōtō is extremely bloodthirsty, which means that once they were taken out of their scabbard, they only could return after their blade tasted blood. Numerous swordsman that touched the Muramasa blades suffered their curse, committing suicide, killing friends and family, or committing other atrocities.
Even if master Muramasa is the most famous swordsmith to work with cursed blades, he isn't the only creator of them. Tyrfing, created by the dwarves Dvalinn and Durinn for King Svafrlami, was a nordic cursed sword, containing the standard characteristic of killing at least one person every time it was used. Mars, a Roman god, had a cursed sword forged by Vulcano. Mars's sword was stolen by Attila the Hun. Is possible that the sword is Joyeuse, Charlemagne's sword. The true Joyeuse was lost and a copy was kept by the French crown. Four swords only known as "Four Horseman's sword" are also yōtō, but their existence is unknown, as their smith.
Some people tend to blame the materials of this kind of blade for their characteristics. Stygian metal, iron alloy nuggets obtained by placer mining the River Styx, are commonly used for cursed swords, as the Styx have natural cursing powers. Cold iron, another anomalous iron alloy, is the second most used material for yōtō as an already cursed material. Beryllium bronze and orichalcum are often used for their high thaumaturgic conductivity. Other common materials are red mercury, electrum, and bones, mostly human or fae bones.
The process of creation of a yōtō is highly covert, as they tend to be too powerful even for their creators. An admitted step of forging this kind of weapon is that the swordsmith has to present wrath in their heart, a feeling that will pass to the arm while it's being forged. Usually, the designer of the hellion blades are rageful themselves or are targeting the first owner of the blade with their hate.
Muramasa's Blades
Indeed, master Muramasa was notorious for his love of deadly weapons. He and his master, Gorō Nyūdō Masamune, have a well-known story about a challenge between both of them. Professor and apprentice forged their best swords. Muramasa's sword was named Juuchi Yosamu2 and could cut anything in its way. Masamune's sword, the Yawarakai-Te,3 at first sight seemed to cut only leaves. The reality is that Yawarakai-Te had the capacity to discern and chose what to kill and what to spare. Juuchi Yosamu was bloodthirsty, thus considered evil, a yōtō. This narrative is sometimes classified as a myth to explain the foundation of the Muramasa School, the only fully anomalous swordsmith school of Japan, but also resumes what to expect of a demon sword.