Transported to a previously thought fictional world, with foreknowledge and superior powers, do you feel dutybound to help the protagonist fulfill their quest, or do you feel that you must stay out of the protagonist's story?
The only moral response is “defeat the demon king on your own immediately, saving a sizeable number of people in the process,. Anything less would be immoral. Morality is more important than somebody’s chance to be a hero. They can go be a hero somewhere else.