What genre might 'watcher based on a true story' belong to?

Well, it could be a thriller. If there's a watcher involved, there might be some sense of mystery and danger, which are typical elements of a thriller.

It might be a drama genre. Given that it's based on a true story, it could be about the emotional and interpersonal relationships of the twelve people. For example, if it's about twelve family members dealing with a family - related real - life issue, it would be a drama.

Maybe it's a documentary - style work. Since it's based on a true story, it might present facts about Nathan's life in a non - fictional way, similar to how documentaries are made. It could include interviews, real - life footage if available, and a narration of his story.

It could be a horror genre. Since it involves the concept of being 'possessed', which is often associated with scary and disturbing elements like the loss of control over one's self, and the presence of some unknown and potentially malevolent force. This is a common theme in horror works.

It could be a thriller. True stories often have elements of mystery and danger, and when a stranger is involved, it can add to the suspense. For example, if the stranger is linked to a crime or some sort of secret.

It could be a thriller if the 'swarm' represents something menacing like a swarm of locusts or a group of criminals.

Maybe it's a documentary - style work. Given that it's based on a true story, it could present the facts about the undershepherd in a more factual and educational way, much like a documentary would do.

It could be a drama. Given that it's based on a true story, dramas often explore real - life situations and the emotions associated with them.

It could be a crime genre. Since it's based on a true story, it might involve real - life criminal activities and investigations.

It could be a drama. Given that it's based on a true story, it might deal with real - life emotions and conflicts, which are typical of the drama genre.