Hanae Ashiya's transition into high school has been far from perfect. For the entire first week, he has been confined to the infirmary with a mysterious illness that only seems to be getting worse thanks to a strange and fuzzy creature that attached itself onto him just before school started. In search of a cure, Hanae finds a flyer for an exorcist who claims to have the ability to banish wandering youkai. Without any other options left, he contacts the number on the flyer and is brought to the Mononokean, a tea room located near the infirmary. There, he meets a somber man named Haruitsuki Abeno who begrudgingly agrees to help him, but only if he is willing to pay a steep price for his services. With no choice but to accept, Hanae is forced to work off his debts for the Mononokean's boss, who also happens to be one of his new classmates. Now, in order to free himself from a future of unpaid dues, Hanae must team up with Abeno and confront the perilous youkai world, leading them back to the Underworld one by one.