Sekai ni Hitotsu Dake no R

It's tough being a ghost in the modern era. A group known as "The Seven Wonders" are distressed by the lack of children taking tests of courage to the school that they haunt. Without children who believe in them and perpetuate ghost stories, they will eventually cease to exist! Can they figure out how to instill fear in children, or is the modern world already scary enough?

In a world ruled by chaos and darkness lives a warrior whose family was killed by demons, his name is Urus. Driven by madness and revenge, one day he hears of "Kelg's pub", a place where heroes who were reincarnated into this world go to search for companions in their quest to defeat the demon king. Wanting to be chosen by one of these heroes urus makes his way to this pub but... There he is labeled as the weakest class by a strange summoning ritual and branded with the mysterious letter "R". It is here that he comes into contact with the true darkness of this world. What is "R"? What is this ritual!? And what is the darkness of this world!?