If you could have any video game weapon...

Once it gets to level 50 you can use it as an equippable weapon. It's damage is equivalent to it's level, making it one of the three potentially strongest weapons in the game.

And yeah, it changes form after 50, as well.

Coolness. Right now I'm powering up my Muramasa by whipping daggers at Octopi; how high can I get that thing anyway?