Sounds good. Here are some suggestions that you can take or leave:
The {Akane, Rin, Erika, Nene} quadruplet leads to a combinatorial nightmare as implemented by the game (15 possible combinations). I would try to combine some of the paths to save yourself from headaches. Just preserve the ones you deem most important.
If you let lowercase be fit and uppercase be fat, then potentially something like:
Akane Feeder route will always lead to Rin and Erika being fat. (aRE).
- Akane will fatten up Rin even if she’s fit in this route
Akane Fat + Erika Fat route will always lead to Rin also being fat. (ARE).
- Erika will fatten up Rin even if she’s fit in this route
Akane Fat + Erika Fit route can lead to Rin being fat or skinny. (ARe, Are).
So you have your route where Akane is the feeder (aRE). The route where everyone is fat (ARE). The route where Erika is the feeder to everyone (ARe). And the route where Akane is the feedee to everyone (Are).
Then Nene can be fit or fat leading to 8 possible endings instead of 15.
You could also replace Chika with Rin in the house. Rin can be a corrupting force to Akane if she remains fat or a source of teasing if she decides to get fit again.
The other girls (clothing/temple/park/work) operate independently from the main route, so the branching factor is low there.