the basic plot is that MC bases his villains from his novels off of his cat, and then he gets transported into those novels. The villain then turns out to be his cat who has been waiting for him. (there's a time travel element in it too-)
https://www.webnovel.com/book/transmigrating-into-a-book-to-become-a-dog-slave_21218703806867705 (this is just something similar btw it isnt actually it)