The name comes up a lot in video games and anime, and is
derrived from a famous Japanese legend about a swordsmith named Masamune.
Goro Nyudo Masamune lived during the late 13th to early 14th century, and was
considered to be one of the - if not THE - greatest Japanese swordsmiths of
all time. (Do not confuse Masamune with Muramasa or Murasame, as these are
all completely different legends that have attained something of an "urban
myth" status in video games and anime.)