i really liked the concept of this game. I think there's a lot of ways you could explore the 'void' mechanic with a game like this. For example, you could have it so that the void level acts as a multiplier for all damage done to either players, and the game ends in a draw if the void level hits max. That way, players who want to be more aggressive might intentionally run up the void level when pushing to win, but at the risk of drawing to the defender
even some very basic developer card art helps to add flavor to the game. next time, I'd recommend adding some background music too
interesting idea overall, nice job!