Arkannis Major

Arkannis Major, also known as Colony world 4378976.Delta-Four, was a planet located far away from Earth that was colonised by humans some time before the 30th century. Its inhabitants knew it by many fictional names, such as Journey's End, Discovery, and Pioneer. Due to micro-organisms in its atmosphere, anyone living on the planet started to believe things in their imaginations (as well as fictional works) were real, resulting in the outlawing of fiction (in the planet's only city) in the 30th century. (NSA: The Stealers of Dreams)