A kid by the name of Hiruka Sakai has a really important goal to reach. He wants to confront a guy that erased reality 400 years ago. To do so, he has to explore the rest of the world. He can't do that until he shows the citys admins that he can survive in the dark and dangerous world. This is whats called a koro challenge. He also had friends supporting him and MIGHT help Hiruka reach his goal.