Mattsu, Yamma and Moburi - The Mystery of the Seven Gems and the Flying Castle

Mattsu and Yamma are two boys who live in Matsuyama. Their favourite pastime is looking for "the seven wonders of Matsuyama". One day, two men appear. What are the 7 hidden gems that they seek? Moburi, a high school girl who is like an older sister to the boys, also gets caught up in the adventure...