I've had this idea for an RPG where a member increases in weight after an ATB bar fills. You gain access to more powerful attacks the fatter the member is at the cost of a slower ATB time. But you can also cast a spell to decrease weight. So you have to choose whether it's better to have stronger attacks or attack more often.
Like, it may not be worth it to get too fat if the enemy is landing hits over and over in between your turns, and so on.