I Killed the Hero at the Start and Got Forced to Be the Demon Lord

One accidental transmigration. One very dead Hero. Now the entire realm expects me to play the villain. I never asked to become the Demon Lord—I just wanted to survive my first day in this twisted fantasy world. But after accidentally killing the legendary Hero, I'm stuck wearing the crown, commanding monster armies, and desperately searching for a way back home while everyone assumes I'm plotting world domination. Spoiler: I'm really not.