The Crystal Empire, home of the dark, stoic King Shining Armor. As long as anyone can recall, he's always been like this, ever since he was a foal. But after an incident involving several Yak diplomats, Twilight and friends are dispatched to try and cheer the brooding king up.
It doesn't go as planned.

Contains muscle growth, mind change, personality change, straight-to-lesbian (in the second chapter), sex (again, second chapter), and some seriously scary ladies.