In early drafts of Falling, I liked the idea that the protagonists would travel around on a giant flying turtle (I've used this idea for an illustration years ago and always enjoyed the concept), but as the story went along, it felt too much like a plot convenience. It would be much too easy for the characters to travel around and to escape from bad situations. Logically then, the flying turtle was discarded (but as you can tell from the Falling Poster, flying turtles will be around in the world) and became a walking giant turtle, which seemed too slow so it became a creature capable of carrying around 4-6 people. (You can see this in some of my rough sketches).
Sarah and I discussed things and eventually decided that creature felt less of a character and more like a bus, so the creature became smaller and turned into the character you saw in the Falling poster art.
As the characters progressed, the creature was named Nushi, and despite being an animal, she started to develop her own personality, and having a mount didn't suit Paniro's character. There was discussion asking "Does the story still need Nushi?" as I didn't want to force an idea into a story that it no longer had a place in, but Nushi had already turned into Paniro's faithful companion, and part of his larger character arc, so Nushi has earned her place in the pages of Falling. She just probably didn't need to be as big anymore as nobody would be riding her. So what would Nushi become?
Nushi was loyal, soft and friendly, yet capable of being fierce, and also has a tendency to eat things she shouldn't do. Suddenly it became very clear what kind of animal Nushi was...