Glad to see more of Upscale and Rose!

I think you landed on solid characterizations for your characters; for Upscale, maybe the emotional baggage he carries could be that when he was younger he was experimenting with his ability and it lead to a close family member getting severely injured, as in emergency room in the hospital and not discharged until weeks later kinda injured.

As for Rose, I think you made a great call with her not being evil, that might be a little predictable and at the same time, that was not the message I got from the first chapter about who she was, the message I got was that she'll help Upscale with his project and she'll get a meal from it, while tapping into her more mischievous side when enlarged. Kinda reminds me how B_25 likes to characterize Celestia, Luna, Cadance, and Chrysalis in these two stories

Giantess and Devious
Big Celly's Day Off

So all in all, good job so far, you're doing great! Maybe flesh out Rose's character more if she grows next chapter and maybe dedicate a chapter or section of another of Upscale telling Rose or reflecting on the emotional baggage he's endured

At last! I've been waiting for more of this for ages!

[Is crushed by the irony.]

I’m not sure where this is going in terms of conflict, but I’m eager to know more about Rose and why she wants to be giant.

That you put such thought and consideration into this shows great care and attention for what you're aiming for. It'll be sexy, sure, but it's also fun to develop who the characters are, and how they would play off of each other. Not to mention how they'll respond when the size changing starts to happen. I adore that you pressed on with this, and look forward to what will come of it.

Little late to the party, but I just stumbled upon this little vignette via good-old Raps and his art related to this story. I have to say, all the sexy, fetishy stuff aside (and all that is more than fine in and of itself) I actually really love this premise, unironically, from a storytelling perspective. So much so, I registered an account here to talk about it, and I haven't had an account here since I deleted my old one 8 years ago.

You have one character with a niche fetish, the ambition to make a career out of it, and the actual, unique means to do so, and another with a specific, plausible means to fulfill that wish. Both stand a lot to gain from their synergy, but both hold a lot of leverage over each other, and so conflict and growth (of the character kind, not just the physical kind) would come naturally. One is pretty conservative, in terms of not wanting to infract upon the law and wanting to do everything straight laced, and the other is a more of a wild card, who is willing to play fast and loose with the rules. Lack of will power in controlling his ambitions and taking bigger risks at the potential expense of others could serve as a very natural plot point/character arc for Upscale, while the gradual, unintended erosion of moral fortitude could play a part in both his and Rose's stories.

Alternatively, maybe the added attention weighs more heavily on Rose that she ever thought possible, and she's now being pestered by creeps regularly. Maybe her secret identity as a changeling comes out, and that blows back in both of their faces. maybe a casual, sexual relationship with your main star proves to be a damaging form of relationship for one or both of them; they could fall in love, or having a falling out, and that stress of an increasingly small separation between their personal and professional lives is what drives the conflict.

Those are just a couple of the numerous ideas swirling in my head, but the point I want to get across is, despite how bare-bones it is currently, it's already a healthy start to a potential series, and I really think that if you're not currently developing parts 3+, you definitely should. To think, I get all excited about this goofy little premise created in service of getting someone's rocks off.

Can't wait for part three