After the king and his eldest son die, the kingdom of Landor is left without a ruler. Asta, the last surviving member of the royal family, stands in line for the throne. However, before he can claim it, he must fulfill a quest: find the legendary "Key to the Kingdom". Both ancient beasts and a variety of contenders, including a princess, a dimwitted military captain, and a villainous aristocrat, imperil his journey. Someone will find the Key, but will it be Asta? (Source: CMX)

Oukoku no Kagi was published in English as The Key to the Kingdom by CMX Manga from September 19, 2007 to December 30, 2008.