When you were still posting FC and reader started getting sick I def thought Ginger/Champ were putting something in the food to slowly turn Reader into a minotaur too
that's not a bad assumption! it would've been interesting to have it play out that way.
But, if you'd like to know a secret, something that wound up getting cut from the final version (but something that I still personally believe is canon) was Champ's actual motivation. He didn't lock reader in with Jack just to punish them, but rather to starve them. If Ginger hadn't started bringing them food without him knowing (I'd imagine she can fudge the elevator and location logs to hide her activities), then reader likely would've starved to death before Jack would've.
That would've left Jack to have to make the horrifying decision of whether or not to keep himself alive using the only means of... food he had left. Thus fully leaning into the original mythos of the Minotaur. If you catch my drift. I wound up cutting that because it's a little dark, even for me, but still... in my heart, that's the canon reason Champ locked them in. Two birds, one stone, so to speak. Reader would be fully out of the way, and Jack would either be dead as well or he'd permanently lose what little shred of sanity he had left.