That's intriguing, and oddly, I think most of my non-prompt derived fic starts in a similar manner, though rather than, say, a broad element of a character it'd be a particular manifestation of that character trait that's stuck in my head as a particular interaction. And then I have to write the story to justify the interaction. (In fact, I struggle writing porn because I have to know WHY everyone is in the bed and doing what they're doing, and how they got there.) I kind of struggle with plot, because for me it's an excuse to write the character interactions rather than the point of the story, whereas as a reader I'm like OMGWHATHAPPENSNEXT?

Prompts are an interesting exercise, even if you chose not to take them anywhere.