This art style is fantastic! I had a little trouble with the "execute" button not wanting to attack. Maybe I was doing something wrong though.
Many people have this problem. You need to distribute the cubes among the characters first. In the next phase of the battle, you must click on the cube and point it at the enemy, so you will attack the enemy.
I got it! I didn't realize you needed to click on the enemies name to assign the execute cube.
