关元之战百年后的太平盛世；远离京城的东北小藩香山藩所管辖的山村惨遭一夜灭村。九死一生的少年蓑吉逃到了和香山藩敌对的永津野藩境内，获得永津野重臣曾谷弹正的妹妹朱音(内田)的救治。然而蓑吉太过恐惧，封闭了那个夜晚的记忆，无人知晓蓑吉的故乡究竟发生什么事情。不久永津野藩内也发生了相同的惨剧，蓑吉这才忆起那个夜晚的全貌。一只不可能存在的怪物竟现身人世，牠的尾巴扫过之处，寸草不留，牠的血盆大口吞下一个又一个无辜的村民…于是蓑吉、朱音、倾慕朱音的保镖宗荣、香山藩主的侍从‧直弥等等住在山脚，仰望山神鼻息生存的人们全被卷入了这场难以理解的灾厄。卑微的人类究竟应该如何面对突如其来的终极灾难？这只怪物又是为了什么，才在此时出现？一切都得追溯到数百年前的两藩纠葛…

It has been 100 years since the Battle of Sekigahara. The Nagatsuno domain and Koyama domain at the southern edge of Tohoku have been at odds for a long time. Soya Danjo , the Nagatsuno domain’s chief retainer, keeps invading and plundering the Koyama domain. His deeds trouble his sister Akane. One day, a young boy from the Koyama domain is covered with injuries after being attacked by an unknown monster. He escapes to a Nagatsuno village and is brought to Akane by the wandering samurai Sakakida Soei. The approaching monster strikes fear. Together with Sakakida and painter Kikuchi Enshu, Akane musters wit and courage to fight against the monster and uncover the mystery of its birth in order to protect her people.