I started writing fetish stories because practically no one wrote what I wanted to read. As a reader, the fetish material:
Must take place on in the story.
- Someone already grown, shrunk, expanded, bimboized, what-evered doesn't count. This is about transformation. If it's over, the reader's been robbed. If you want this character to count, at least provide a flashback.
- It should happen on page. In a story this is the atrocious, "And then her tits swelled up to DDs" or the "When she woke up...". In a comic, the transformation must be shown. If a character walks through the door to the massive boobies room and walks back out next panel with massive boobies, there better be something else coming along or it's not a BE story. Transformation took place, but the reader didn't get to see it.
Must not be a logical side effect of another transformation. Yes, boobs grew in a giantess story, but so did the rest of her. If the ratio of boob to body is unchanged, it's not a BE story. If Janet is a giant because she's now 9 feet of Hulk-class muscle, probably not a giantess story.
Must be integral to the story. The whatever and its aftermath are the focus of the piece.