It was neither a horror/ action/ mystery, nor a sci-fi. It has no theory or story.
This drama was nothing but just a simple game. You may go for it if you want to watch something like blood shed only. There is nothing more. They're just playing mafia game till the very end, every day 1 or 2 students lose their lives and when someone is left alive to finally escape then BOOM! they all were just dreaming and playing mafia games several times in their dreams. The masterminds were their classmate's parents who wanted to take revenge of her suicide and that too by programming. They have created anything whatever came in their mind and named it as drama.