Thank you so much for playing and for the detailed feedback!
The "0" is the city's broadcast "lucky number of the day". The broadcast is there to check whether everyone follows the lucky number, and since you don't, the guard robots attack you. This was my first game jam, so I started with a big scope and had to cut a lot along the way, and I think that made this part hard to get across.
For fighting: the number in front of each enemy's face shows how many strikes its next combo has. Count them, and left-click right as the last strike lands to parry. After the combo, the enemy pauses, and that's your opening.
Could you tell me where the dark block was?