After two major incidents involving Mononoke—it seemed as though peace had finally arrived in the inner palace. However, the medicine seller still sensed a lingering presence of "something" and remained vigilant. Meanwhile, hoping to change her formal marital relationship with the emperor by giving birth to an heir, Sachiko finds herself at rock bottom and becomes embroiled in a terrifying plot that threatens to overturn the very existence of the Ooku. At the same time, unnatural earthquakes occur frequently within the Ooku. A mysterious incident begins with the creepy movement of a gigantic, crawling creature and the falling of triangular scales. The truth behind the monster lies in Ooku's past, 150 years ago.