Yes, it was an original story. The concept of 'The Purge' introduced a unique and disturbing dystopian idea of a society where all crime is legal for a set period of time. It had its own distinct plotlines and themes that hadn't been explored in quite the same way before in mainstream media.
There might be a fanfiction where Sam and Dean Winchester find themselves in a town during the purge and have to figure out a way to stop a powerful supernatural being that is taking advantage of the lawless night. They could team up with some local survivors who have some knowledge of the supernatural.
Yes, 'The Purge' is loosely based on some real - world concepts. For example, in some areas, there are periods of lawlessness or high crime rates that can be seen as a very, very loose inspiration. But the movie takes it to an extreme with the legalized annual purge.
The 'the purge novel' could be about different aspects. It might focus on the psychological impact on the people who live in a society where there is a purge. It could tell the stories of survivors, how they cope with the fear and violence during the purge period. Also, it may explore the political or social reasons behind the existence of such a radical system in the fictional world.
Well, 'the purge fanfic' could be centered around creating new characters within the Purge universe. For example, it could be about a young rebel who decides to fight against the system of the Purge rather than just hide. Or it might explore the moral dilemmas that people face during the Purge, like whether it's right to kill in self - defense or to protect others.