Wellllll, Kotetsu is technically not a cat now but he used to be one┐(´ー`)┌? Soooo I guess he was only left behind with the major characteristic of a cat. He was a cat beforehand sooo he "acts like" a cat but cannot act in a way that a cat can actually do it. For example, that part where he was trying to walk through a very narrow path (I think those were the railings??) He wanted to do the same thing a cat would do (cat walk through it perfectly and not fall off) but in the end since he was a human now (with cat features) he cannot do the very same.
Sorry, my explanation is way too kray kray༎‿༎ but I wanted to express my thoughts on this matter as well
How is he eating chocolate and tucking onions and other stuff that's toxic to cats (garlic, tea, coffee, etc.)? I guess when he turned human, his digestive and other systems also switched over 100%? (눈_눈)