After six years, Tooru and his little sister, Natsuha, returned to the remote village of Monobeno, deep in the mountains of Kochi prefecture. They reunited with the Akashaguma (child-like Yamori Youkai) Sumi, the Kasayou Hishakaku, and his childhood friend and self-proclaimed fiancée, Alice. They played in the mountains, visited the shrine, and were visited by the Ushi Oni Tooko, just like in the past. Just as they were getting used to living in Monobeno, it was time for the Shichi Seisai summer festival, dedicated to the local deity Himemiya-sama. The festival was lively, concluding with the masked dance. While watching the dance, Natsuha suddenly started shaking, complaining that her body felt cold. Tooru quickly took her to the doctor, but nothing seemed wrong with her. They went to play in the nearby stream the next day. Hearing the waterfall caused Natsuha to panic and run off in fear, but they couldn’t find a reason for her peculiar actions. That night, she appeared in front of them as an adult and bled in her nether regions for the first time. Unable to figure out what caused these inexplicable changes, they could only calm her down and watch over her. When they woke up the following day, they were shocked to see Natsuha was back to her normal size, but she didn't remember anything about the day before. They decided to head back to the city for a proper examination. Unfortunately, a major landslide blocked the only access to the outside world. Natsuha wished to leave badly, saying something scary was coming for her. What was causing Natsuha’s changes? Was it a disease or a curse? Tooru was determined to find the cause and a way to save his little sister.