After a gruelling final tour, Aurélien decides to settle in Japan with his wife Nanako, who is pregnant with their first child. As the young couple move into a traditional house in the Japanese countryside, Aurélien discovers an ancient suit of armour in a well, which is about to awaken strange creatures known as Yokaïs.

Nowadays, in a France where the monarchy has never been abolished, a plane crash costs the life of the entire royal family. Samia, a naive teacher without authority, learns that her son Cédric, a simpleton teenager born of a temporary union with a nobleman, is the heir to the throne. Now named Louis 28, Cédric has many projects for the kingdom such as "the abolition of math", but he will come up against the directives of a retrograde regent and ready to do anything to trip him up. Mother and son are thus propelled into a courtyard where these "toothless" are the object of all treachery.