Well, the grind/repetition is certainly for real (downloaded this yesterday and have pretty much been playing it non-stop since, finally got to the end just a few moments ago), but damn if I didn't enjoy almost every second of this XD
That would be your boss, Rebecca.
The MC isn't making her exercise, she herself is exercising mostly of her own volition. A large chunk of the game is spent with you trying to get the girl to gain without her realizing it, so she keeps working out because she's worried about how big she's getting. Eventually there's a point where she realizes the MC is purposefully fattening her, and things play out from there.
I don't think you reached the end of the content. There is a series of screens that tells you when you've hit the end, and that you can continue but everything beyond that point is just repetitive and potentially bugged. Stuff does eventually happen with her getting the job, it just takes quite a while in game (at least in my experience) for this to actually begin.
That's very unfortunate, and I know you aren't the creator/are just a fan but in the off chance they read this: please don't give up on your project. It's clear to me that you put a lot of heart and passion into this, and it does suck that it was pirated. But in a way, this also serves as an advertisement of said project - I had no idea this game existed, and I never would have if it weren't posted here. This was a far better experience than I expected, and I am honestly most likely going to subscribe to their Patreon (provided they do continue development) to support the development of this game, despite generally being broke and not ever spending money for things like this LMAO. Hopefully, an influx of support might be the silver lining to this happening?