Muramasa Sengo was a swordsmith in 16th century Japan. Though an excellent swordsmith, he was said to be insanely ill-tempered, verging on just straight-up insane. This trait led to myths that swords made by him were [[{{EvilWeapon}} cursed with the same afflictions]], encouraging the wielder to fight to the death, and would, if no battle was present, turn on their owners and [[{{DrivenToSuicide}} compel them to commit suicide.]] These rumors weren't helped by the fact that Shogun UsefulNotes/TokugawaIeyasu banned Muramasa blades because many of his friends had been killed by them, and that he had accidentally cut himself badly with one (after all, history is WrittenByTheWinners).

In fiction, Muramasa will usually be a rival of [[http://en.wikipedia.org/wiki/Masamune Gorō Nyūdō Masamune]] (Masamune). Never mind the fact that [[ArtisticLicenseHistory they didn't live in the same time period]]. A legend regarding both swordmakers said that they held a competition to see who was better by putting one of each of their blades in a stream. Leaves floating towards the Masamune would drift safely around the blade, while the Muramasa drew leaves to the blade, whereupon they would [[AbsurdlySharpBlade slice themselves in half]]. Muramasa bragged that this was evidence of his sword's superiority since Masamune's failed to cut anything, but Masamune stated that Muramasa's blade was inferior since it cut indiscriminately without control.

Muramasa's swords, which are often named after him, will usually be AlwaysChaoticEvil, [[{{EmpathicWeapon}} Empathic]], [[AxCrazy bloodthirsty]] - possibly even [[HungryWeapon absorbing blood into the blade to strengthen itself]] - or [[OurVampiresAreDifferent encouraging the host to do so by cursing them.]]) and have an ObviouslyEvil appearance aura about it (Notches, rust, bloodstains, ect.) The blades may also take near inhuman force of will to sheathe the blade once unsheathed [[DrawSwordDrawBlood until blood is drawn with it]]. In sharp contrast to the swords made by his rival, Masamune's swords can be more reliable, but [[WillfullyWeak less overpowered]].

If a work features the swords of both, expect the Muramasa (or its user) user to be evil, or at the very least, [[{{AntiHero}} morally grey]], and the Masamune (or its user) to be good ([[VideoGame/FinalFantasyVII most of the time]]).

Neither are to be confused with Murasame ("Autumn Shower"), another popular name for fictional katana, which is drawn from a magic sword in ''Literature/NansouSatomiHakkenden'' or one of the protagonists in the Noh play ''[[https://en.wikipedia.org/wiki/Matsukaze Matsukaze]]''.

For examples of these swords in media see PublicDomainArtifact.
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