Actually it seems that in the lore of Japanese swords and their smiths, Muramasa is a name of ill-omen compared to Masamune, said to be his teacher.
"MURAMASA, The Cursed Sword smith
The other sword smith named Muramasa was a Japanese student studying the art of sword-making under the guidance of Masamune. He wished to recreate Masamune's work, but failed. In the Japanese bujutsu there is a saying: satsujinken katsujinken. Roughly translated, this means 'The sword that kills, the sword that gives life'. This principle dominates the entire word martial in that a martial artistís goal is to preserve life with his skill, never to take it.
Masamune knew this, but Muramasa did not. For this reason he did not have the insight on the blade that his teacher did, and therefore could never accomplish the same skill in his own work. He assumed the blade was for death alone, and because of this, his sword smith skills have always been pulled to the satsujinken side of the equation (killing), his blades always wanting blood and never serving their true identity."
This is edited from a possibly unreliable Web source, concerned with manga/anime.
A warning in there somewhere for addicts of tricky joseki?
-> Just a historical note: Muramasa was not actually a student of Masamune. They were separated by a few hundred years.