habits rubbing off

[riptoryx]

Hm. I'm not sure if this will be quite on-point--the weight gain focus is on one character rather than a bunch, for example, and it's not the case that most other characters are already fat--but unintentional weight gain attributable to a variety of compounding "bad influences" without any sort of overt feeder-type character generally squares up with my story, "The Slowest Champion -Revisited-." Academic settings feature prominently, too, if that matters.

And if you haven't already, you might also take a gander at "Downward Trend" by  @maxymumspyder / kowlooner, for similar reasons.