You added the Villain. You added that the Villain is going to kill everyone including the merchant. And you added that the merchant knows all this. I can write 100 stories about a hero who needs a sword without those elements.
You seem to be saying that every character in a story is either a protagonist or antagonist which simply isn't true. The vast majority of characters in almost anything I can think of are neither. Unless it's a story with two people in it. What is the definition of antagonist you are using? Because it doesn't align with the definitions I know.