It is the late Edo period. Futaboshi Hikoma, the Hirado domain's astronomer, is a rather eccentric person whose only interests are the stars and sea. A beautiful bride Orie comes to him and Hikoma vows to himself to cherish her in his lifetime. However, in less than a month, his new wife disappears without a reason from this dreamlike married life. In truth, Orie is a female ninja that the shogunate has sent because of its suspicions about the domain's illegal trading and activities. The shogunate plots to punish and destroy the Hirado domain in a warning to various domains in the west. Not knowing this, Hikoma goes to Edo in search of his wife. He is introduced to Matsuura Seizan, the former feudal lord of the Hirado domain, by his old friend Senemon, but is told by Seizan that he will slay Orie if she appears. Hikoma declares that he will be his wife's shield if Seizan insists on snatching her away. In order to find Orie, Hikoma becomes an instructor at an elementary school and meets a boy called Tarokichi. On the other hand, queer phenomenon in which festival music can be heard occurs at Seizan's residence each night. Hikoma sees fireballs with his own eyes and starts to delve into the mystery with the school children. However, this gets them close to the heart of the shogunate's scheme...