Maggie loved these derpy looking tigers from Korean folklore illustrations, and then Helen did some awesome concept art for what they could look like. I took point on creating an on-screen persona for Derpy & Sussie to figure out how the cat acts, sounds, teleports as a messenger that would not only disarm Rumi's concept of demons, but also be a way for her and Jinu to share secret messages with each other that could build the relationship (like a shared pet).
Mostly, these personas were just based on our own cats "Mr. Meowgi" and "Cleopawtra Jones", a brother and sister we adopted as kittens. Meowgi was extremely clumsy as a cat, and his sister, the perfect graceful cat would just watch him in shame.
This is an initial thumbnail pass of that process.