Thank you! I'm happy to hear you found the meta use of the theme to be of interest! Regarding the time frame, the graphics and implementing all the mechanics took the most time. The audio was completely rushed on the Saturday before the end of the jam, but I tried to do the best I could in the time I had.
About the cave and the light. I intended for there to be a bit of a struggle, but not for it to be reliant on player skill, or to be frustrating. The game hand holds the entire way up until that point. I wanted the player to have to do some work on their own, and to convey a feeling of going from easy to "oh crap", and finally back to the happy ending again. However I'm thinking the use of a darkness mechanic isn't the best way to accomplish that.
Regarding the input, yeah... Arrow keys would of taken two seconds to add. Completely spaced on it, rushed adding the key binds. My fault.