Mattsu to Yanma to Moburi-san: Nanatsu no Hihou to Soratobu Oshiro
English name: Mattsu, Yamma and Moburi - The Mystery of the Seven Gems and the Flying Castle
Genres: Fantasy
Type: ONA, Episodes: 1
Aired: Oct 1, 2013
Source: Unknown
Rating: G - All Ages
Synopsis:
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 as this thriling story set in Matsuyama begins.

Faced with all kinds of trouble, what will they choose for the future of their city? 

(Source: Official Site)