In the year 2005 a race of alien monsters emerge from underground and launch a series of attacks on the city of Tokyo. The only defense against these creatures is the awesome giant robot GaoGaiGar and its pilot, Guy Shishio.

In the year 2029, chemical elements such as oxygen, carbon, gold, molybdenum, and cobalt were continually disappearing from Earth. These disappearing elements ultimately disrupted the environment and led to the destruction of various homes, cities, and even entire countries. Researchers discovered that the vanishing elements drained into a planet called Nega Earth, located in another dimension. Element dematerialization was occurring rapidly; thus, to save Earth, three special pre-teens picked by the space colony government formed the Element Hunters. Their job was to transport themselves to Nega-Earth to battle monsters called Q-EXes and retrieve lost elements. However, out of their own concerns, Ren, Chiara, and Homi, three average middle school students from Earth, banded together to also become Element Hunters. With the help of Professor Aimee Carr and Juno, they are able to help save their own planet.

Inspired by 90s genre shows like Buffy, The Vampire Slayer and The X-Files, Demon Doctor is an LGBT story about a portly demonologist and a detective who believes in the beyond teaming up to confront the mysteries lurking beneath the surface.