A spa in the shopping district that allows you to spend gold to lock your character for a set duration and gain an amount of energy. Maybe a cute animation while they are locked in the character selection screen, like floating on a cloud.
This idea could provide players a new opportunity to gain the precious energy resource as well as encourage them to work on other characters. Or touch grass.
Touch? Grass? What do you mean? Also I'd be worried about locking characters because I want to get my special event and scroll of fortune points, but I like the thought of going to a spa for energy.