The story of how it was forged was there was to sword makers, Masamune and murasame, his apprentice, who tried to outdo his master so they both forged the best sword they could.
When it was done, and they saw there creations they had a contest to see what was better. Murasame lay his sword down in the steam and a leaf came past, and it cut it clean in half. The masamune was placed in second into the stream and another leaf came down. Strangely enough the masamune cut the water, Obviously masamune was baffeled by this and asked why did it happen.
Masamune said My sword knows its true purpose, to defend life - not to take. it cut the ater to prevent uneeded distruction, your sword does not know this and thus it can never reach its full potential."
so meh. random really...