Love this game!!!
In terms of gameplay, I don't think I can add anything that hasn't already been said. But visually I would suggest giving more feedback to the player, for example when the dragon comes maybe add some screen shake, or add little animations or just change sprites for when the king's reaction to things. Maybe even stars at night or a sunset at dusk.
Essentially just subconsciously let the player know they made a difference to reinforce the player's experience.