So this was fun. Start with a design from Thingiverse, use netfabb to slice it into bits, print, and paint. The "blade" is a simple separate design, sized to fit in the hilt piece and made from glow-in-the-dark blue filament.
But the pommel? It comes off. It stays quite snugly on the USB plug.
And I'm sure you can see what's happening.
That's a pair of UV LEDs powered by the USB drive. And since it's the glow-in-the-dark filament, it keeps fluorescing gently for a while after the drive is unplugged.