Similar to a light saber but more Nintendo-y, this DIY beam katana seems to be an actual working device, although I question its lethality. The creator won’t reveal his secrets, but I think it’s pretty clear there’s some kind of little smoke generator and one of those green high-powered lasers involved. Get a couple more high-powered ones or a mirror setup in there and you could actually start burning through some junk, though admittedly not at a true beam katana rate.
Here’s another video, with some cosplay thrown in there for good measure:
He looks like the kind of person my mom warned me about.