Is there a antagonist in "The Chaser"?
Yes, I suppose one might say that the antagonist is the young woman with whom the protagonist Alan Austen is in love. She does not appear in the story, but her importance is obvious. He loves her but she doesn't love him. He has undoubtedly tried other means of getting Diana to fall in love with him. (She is appropriately named, because Diana in mythology was a virginal young goddess who could not be won by any man.) We can tell that Diana must be a strong antagonist because she is so difficult to win. The old man who sells love potions is the lover's last resort. He will help Alan win Diana but expects to make a big profit in the long run. Presumably Alan wins the conflict with Diana. The old man is neither the protagonist nor the antagonist. He is an amused observer. He has seen the same conflict many times before. The story ends with Alan exiting the shop with the magic love potion and the old man saying, "Au revoir," or "I'll be seeing you." But it is the conflict between Alan and Diana--that drives the story. A protagonist does not necessarily have to appear in a story, nor does an antagonist, although it might be impossible to find a story in which neither the protagonist nor the antagonist appeared as a character.