I'm not sure why they exist. But, as Japanese site IT Media points out, they do. And what's this tech demo called? "Oppai Motion," or "Boob Motion" in English.
Warning: This article contains content some readers might find objectionable.
As you can see in the below video, the demo uses the Leap Motion gesture input device to, I dunno, become abreast of the tech. Whatever the reason, the end result is pretty creepy!
The developer who created this demo has put the source code online. It would be surprising if Leap Motion, for better or worse, wouldn't find a ready audience among adult PC game players in Japan.
ついに2次元キャラのアレをもめる技術が開発される [IT Media]