Thanks for playing and reporting the experience. Yeah, some story elements should be in the game, I'll see to that. I'm still focused on exploring possible mechanics extensions that utilize light/shadow dynamics.
The objective is literally written at the start of the run, extending the title ;) But I think you picked everything up quite quickly. You need to shut yourself into the darkness. The game was done for a jam whose theme was Isolation. The ultimate why is left to player's interpretation. Perhaps you're a vampire and need to go to sleep :)
The inverted mouse is default simply because it's my personal preference. Since game still doesn't save any settings on the user side I just kept it inverted for easier testing. Will swap it to the standard non-inverted default.