Ay guys, I have been overthinking the overall worldbuilding in the kipverse lately, specifically how society views weight gain and fat, how the official lore explains it, and why there is such a massive gap between public stigma and widespread attraction to fatness, stuffing, and all of that.
So: in early history, humanoids in this universe likely evolved in harsh environments where food was very scarce. Their bodies evolved and adapted to process food in the most efficient way possible, storing energy not needed at the moment as fat, but WAY faster and in FAR larger quantities than real worls humans (very efficient), making it possible to gain a lot of weight and fat within days, and also developed high stomach elasticity in order to handle massive calorie intakes whenever food was available. HOWEVER, when civilization progressed to agriculture, cattle, and other forms of early food production, famine slowly vanished until by the time modern society came to place, lack of food wasn't an issue for the average person. But because food became abundant, rapid weight gain transformed from a natural survival mechanism into a heavy social mark of laziness and overindulgence: if you eat a lot and don't participate in manual labor, you'll get fat, naturally, and even more so if you are of the same species as the population in the kipverse.
And this is where the whole feather ears deal comes into play. If you look at that official lore sheets, those feather ears are literally connected right into brain tissue, acting like natural displays for your health, discipline, and standing in society. Gaining weight easily is explicitly listed as a negative physical trait by their culture (due to the reasons i listed before), which suppresses feather growth and/or makes them fall off, unless counteracted by crazy mental effort, some form of high social standing or an enviroment where people don't shame each-other over their appearance (impossible in the kipverse lol). Plus, how well your feathers hold up depends heavily on the people right next to you, not distant followers in social media. That's why Tessa molted so violently and fast. When she surrendered during the belly massage, it was not distant online followers making her lose feathers, it was the immediate shock of being judged in real time by those fifty classmates physically present in the room, triggering a massive stress reaction on her feathers regardless of how she was feeling at the moment that made them shed instantly.
Since losing your feathers basically ruins your social standing, everyone enforces this super harsh anti-fat culture. But because their biology is naturally built for indulgence, and this could've easily been a sexy trait in early history of this world. Fat body? Great hunter and provider of food, strong and healthy children, etc. So i think that being into fatness did not vanish, it just exists as this massive underground niche. Attraction to fatness in this world must super common, due to biology and the appeal of what is prohibited or seen as "wrong", but social risk forces a lot of people to hide it or act out against it. We see this with Stacy and Aika. Stacy was a total bitch to Aika for a long time, theh didn't get along at first, to the point that they had a fist fighting during an oral presentation lmao. It took forever for them to even get on somewhat friendly terms, and Stacy only acknowledged her feelings for Aika one or two hundred pages ago some time after Saiya cheated on Aika with Tessa and fucked everything up even more that it already was. Stacy watched all of this unfold and could not believe Saiya blew it with such a great girl, and when Saiya eventually called her out on loving Aika, Stacy was embarrassed as hell but could not deny it. And now we just saw Stacy eventually letting herself indulge in Aika's massive stuffed belly after alcohol lowered her guard, so... yknow.
We have also seen different angles of this with other characters across the comics. The protagonist of No Lunch Break did not let go of her childhood memory of that swimsuit girl with the fat belly at all, she was always completely aware that she was into fat bellies and fat people. She just had not explored it sexually until she left the hospital. Once she saw herself fatter than she had ever been, she embraced the fetish full time and started obsessively stuffing herself, even enjoying the stares and comments from onlookers. Then you look at the first comic, Breakfast with Sister, and the sequels Lunch with Sister and Dinner with Sister, where the protagonists are pretty much all open enjoyers of food, gaining weight, and fattening others up. What I'm saying is that it shows that even with all the heavy social stigma pushing people down, the biological pull toward fattening and being fattened is always right beneath the surface, waiting for an opportunity to break out.
Anyway, that is pretty much my theory. What do you guys think? Though to be honest, now that I finally put it all into words, maybe it is actually a pretty simple conclusion to reach lol