Fading out all but one object for VR


I want a player to start in a pitch-black environment. A ball of light appears drawing the player’s attention in a certain direction. The ball of light flies away into the world as the scene fades in.

I’ve looked into a solution with UI canvasses but I’m afraid this doesn’t suit my specific situation as it doesn’t let me show the player the ball of light. Any ideas on how to achieve something like this?

Maybe having an unlit black cube around the camera and setting the transparency of the material (I do fading this way)… but it depends of how close you are to the world, and how far away you want the light to travel before fading in… the light would have to be inside the cube… maybe it could work…