What I think is the cat most likely using(?) Wanyi to cover the villain role, the cat probably noticed that he's different than the rest and had a mind of a potential villain or just manipulated(?) Wanyi feeling of guilt being the 'lone survivor' and since Wanyi wants to revive everyone, he accepts the System's offer. But the cat is just following the System so I don't think we should look at the cat as to whether they're good or evil since both sides benefit, the cat uses him for the plot stories (though I don't know why they exist) and Wanyi, once he got enough points, will be able to revive everyone.
(dunno if this helps but I hope this can make you understand even a bit haha)
Just a wandering lazy simp reader~