I already touched on part of it here. I think this excellent story captures the limit to which I want extreme weight gain realism to go. In the realm of fantasy, “extreme” is subjective, particularly in the world of weight gain (some people are into the planetary proportions, after all). Ultimately, I find the attraction to extreme weight gain in the size of the rounded curves and rolls, the adipose physics, and the sheer weight of it all. For me, the negative health consequences are great as long as they are limitations and obstacles, not insurmountable challenges. That is why I draw the line at immobility.
Perhaps unlike most in this kink, I do not care for intentional stuffing. Gluttony for the sake of getting fatter is a turn-off for me because it suggests willing acceptance, if not outright embracing, of the health and mobility repercussions. Instead, I welcome overeating out of a naturally large appetite and poor nutritional decisions. The habit should be from a lack of understanding of portion control, not from a love of gorging and addiction to the food coma.
I think it is important that you distinguished this thread as pertaining primarily to fictional depictions. Fantasy is critical to my enjoyment of extreme weight gain for two main reasons. First, people’s bodies in real life often react in unappealing ways to extreme morbid obesity. Proportionality is off, skin complexion suffers, and cellulite deposits can create ugly lumps. Second, superchubs appreciate their physique, while I like to observe the morbidly obese that are ashamed of their size. The ultra-fat that are embarrassed of their bodies rarely document their struggles, and those that do often have underlying reasons why they are overweight (e.g. family trauma, eating disorder) that interfere with my enjoyment of them.
Side note: I am drawn to the internal relationships: one’s relationship with their lifestyle choices and their body. As a result, I have a difficult time finding weight gain literature that caters to my interests; the fictional weight game genre often centers around dom-sub feeder-feedee relationships.