You've adventured your way through your fantasy world. You are among the best in your world a paragon of your particular approach to adventuring. The mightiest warrior, sneakiest thief, craftiest wizard... etc.
Well, what now? You've reached your highest dreams. you are the best there is... You are bored.
So when a crazy sounding traveller from another world came with a proposition - an adventure suitable only for someone as esteemed as you, you were hooked.
Welcome to a new world. You know nothing of it. It has unknown challenges. You don't know where you fit. You have been warned - magic is unlike anything back on your world (good luck spell casting types!). Go forth. Adventure, prosper, and fight back the ennui of a long career. Death to the red dragon!