It fits the fantasy genre as well as the horror and survival genre.
Nightfall takes place on Mercury, on an island called Bliss where night and day are both 14 years long and where humans have to leave the island during night, preparing their houses to look exactly like when they found the island.
The main characters, Marin, Kana and Line, are left behind on the island because of a coincidence and they´re trying to find a way to leave the island as soon as possible.
However, they expected to be the only ones left on the island until they are attacked by some dark creatures.
While trying to survive the island they have to face their fears and learn how to work together so that they will survive.
I personally thought the book was really great and thrilling despite people saying that they thought the book was boring. It was super different from any book that I read before which made it a book that I enjoyed reading.
I was also pretty surprised that this book actually works with the feeling of the reader while reading it. With that I mean that if you really feel the book (Example: like when you realize that they can´t just wait a few hours until it´s the next day to leave the island) then I´m pretty sure that you will like it probably as much as I did.