First, study the different cultures in The Last Airbender world like the Water Tribes, Earth Kingdom, Fire Nation and Air Nomads. Their unique clothing, architecture and symbols can be incorporated into your OC's design. For example, if your OC is from the Water Tribe, you might give them blue - toned clothing and jewelry inspired by sea creatures. Also, consider their bending ability or lack thereof, which can influence their appearance. A non - bender might carry more practical tools, while a bender could have accessories related to their element.
Avatar: The Last Airbender is indeed an original story. It has its own distinct style and narrative that sets it apart. The combination of elements like bending powers, diverse characters, and complex story arcs make it a one-of-a-kind creation.
Definitely not real. It's a fantasy world crafted with unique characters and magical elements that exist only in the realm of imagination and storytelling.