We recently framed a gas pump nozzle (17 lbs) and used modified offset clips screwed through a hole in a wood backing, which we first covered with mat board. The clips were modified by a welder. It was amazing how well it worked and how easy to mount. Time to figure out how to mount the nozzle? Hours. The finished product? Priceless.
The handle end may be mounted with a clear polyester film strap; probably 1/2" wide would be plenty of support.
The business end of it -- sharp, I presume -- may be mounted with a formed rod mount made of spring steel (piano wire); probably .032 diameter would be a good size. To avoid scratching the metal of the sword, pad the mount with shrink tubing. Or, maybe you could use stainless steel picture framing wire as a mount, also padded, of course.