55 parte Kumpleto Sen is an orphan whose only family is Hashioni, a great yokai who has long defended their village from raiders and thieves. When Hashi falls prey to an illness known as The Rot, Sen embarks on a journey to find him a cure before the Rot consumes him entirely. Joined by two Buddhists, a ronin, and a wayward onna-bugeisha, his journey opens his eyes to a world he's never known and reveals that a much more sinister plot may be behind the illness that threatens to kill his friend.
His destiny lies intertwined with Maru, a war orphan whose life belongs to the Sayonakidori - a sect of yokai hunters whose mission is to defend humanity. A contract for a demon who killed the son of a wealthy samurai sets him on a journey that makes him begin to question everything he's ever been taught. When the contract begins to be more than it appears, Maru must decide whether his loyalty lies with the people to whom he owes his life or to himself.
When the two finally meet, their lives change in a way neither of them anticipate in an age where endless war has tipped the balance of the world and calls out for the Disciples of Hachiman, the ancient Kami-sent warriors destined to keep the balance between yokai and humanity.
