The unique character transformations in these stories aren't really about physical change itself. They're a specific, tangible vessel for exploring psychological and relational states that are often too abstract to nail down otherwise. I'm drawn to the genre when it's used as a metaphor for profound shifts in power, dependency, and vulnerability, or the total erosion of a previous self. A character whose literal form is altered, whether grotesquely or with a kind of strange beauty, loses the ability to hide behind a socially constructed facade. That's the real meat of it.
I read one recently where the protagonist, initially a very buttoned-up and controlled person, underwent this inflation not as a violation but as a form of release, a shedding of constraints. The narrative tracked how their internal self-perception and their partner's desire evolved with each incremental change. It wasn't a cheap gimmick; the transformation forced conversations about intimacy that the characters would have otherwise danced around for chapters. The physical extremity becomes a narrative lever to pry open emotional truths that more subtle plots might only hint at.
I guess for some readers the appeal is purely in the fantasy or the visual, which is fine, but what keeps me in those stories is the author's willingness to commit to the consequence of the change, to follow it through all the way to a new normal that's both unsettling and deeply intimate.