Noshiro didn't say exactly how the trick worked, despite curiosity from his followers. However, one person asked him if he fixed the camera to pre-record the background, and he admitted "that's correct." So in other words, he likely first recorded what was behind him, then masked out his face -- bar his eyes and mouth -- and inserted the background. The iPhone X's motion sensors could synchronize everything with the camera movement.

The effect shows the potential of sensor-laden phones like the iPhone X -- which are bound to become more common with Face ID-like security -- and how ARkit can work with other developer platforms like Unity. Sure, it seems perfectly useless, which is why it might also make a pretty sweet Snapchat filter.