The laser harp has been around since the early 1980s, though it still draws attention every time someone plays one. The instrument projects a vertical array of laser beams; interrupt a beam with your hand and it triggers a note. Pluck through several beams in sequence and you have a melody — same basic logic as a string instrument, just with light instead of wire.
This performance plays the main theme from Super Mario Run in playback mode: a backing track runs alongside the live laser input, with the melody handled entirely by the harp. The theme comes through clearly against the fuller arrangement, and the visual element is half the point — watching something as immediately familiar as a Nintendo theme emerge from mid-air beam-plucking is its own kind of strange.
The laser harp unit used here is from Harpejji Laser (harpelaser.com). If you’re curious about how the instrument works mechanically and electronically, the How Does It Work post has the full breakdown.