I feel like it's too late to comment this at this point, but I think a lot of users would really like a fat-phobic personality type across the board.
- A feeder type who degrades you and inversely self degrades in response to their own gains.
And
- A superficial feedee (as well as) a normal fat-phobic type who is ashamed of weight gain and disappointed/repulsed by player weight gains.
This is peculiar in that obviously the theme of the game might make it a little nonsensical that you end up long term partners with someone who is a bad influence on them or doesn't fit their preferences, (regarding the second and third personality types) but could be balanced with tweaks to how much affection and corruption is influenced by the player's actions.
It's definitely an unsavory flavor of the kink, but one I am certain there are many accustomed to and would greatly greatly appreciate!