To add my input, particularly in regards to anothertea’s suggestions;
I disagree with the interpretation that a fit Rin should be exclusively fatten-able during an Akane feeder route. The player, at best, should have the choice to bring her into the feedee category, and at worst, should reckon with the consequence they made by encouraging Rin to resume her fitness endeavours.
Additionally, I find the implication that only one route exists where Rin remains fit to be somewhat anemic in potential. Perhaps initially, yes, to reduce development time of a fleshed out initial release, but Rin has shown to be both a feeder and feedee, depending on the situation.
To put it simply, I understand that it may be appealing for some to see a formerly fat character relapse; To an extent, this is the case with Erika. However, Rin has marginally more player involvement, which both elevates her while also creating potential tension between players who prefer her fit and those who prefer her fat. I find myself in the former category.
To use anothertea’s classification for my own purposes, I advocate for an (aRe) route.