Karma exists. The world rewards or punishes us all. In what way it may come, we may never know. Sometimes it comes to us as plaguing nightmares for crimes we have yet to commit, or sometimes we are just unlucky enough to be picked. It is not fair.
Helleborus, our MC has received both the blessing and the wrath of the world throughout his life of 21 years. He is now given a chance to rise into the skies, or fall into the depths of Hades.
Helleborus was always a person tortured by nightmares his entire life. One day after going to sleep, he is met by a disembodied voice offering him a chance to participate in what is known as the Impossible Nightmare System. As the punishment aspect of Karma, Nightmare System lures people plagued by nightmares into a world of nightmares where they need to survive, torturing them thoroughly. As a new member of the said system, our MC will try to stay alive with all he has.
This isn't a novel where only the MC has a levelling system.