The theme was "duality". We use the duality of the human being. If I have to be more specific, it refers to the reality of some people who have to fight their own war in their minds and try to seem happy outside. That's why you controll both characters at the same time.
You control both using just a pair of keycaps, be careful because the movement of one side is morroring the other.
Each side has is own puzzles, you will have to solve them without jump into the void, because if you do it, the level will be restart.
You only pass the level if both puzzles have been solve.