Thank you so much for the kind words!
You’re right, perhaps I wasn’t clear enough in the tutorial, but the dice assignment is automatic. The system starts by checking the first ability in the stack (from the ability at the top to the one at the bottom) and automatically consumes all the available dice that can trigger that ability. When the ability can no longer be activated, it moves on to the next one and repeats this process until it reaches the last ability. Any dice that remain unused at the end of the cycle are added together, and half of the resulting value is dealt as direct damage to the boss.