The oldest and strongest Dragon who grew tired of living chose to die when a group of dragon slayers came for his life. While the Dragon's soul was waiting to drift toward the Sea of Souls, he noticed it had been reborn into a human baby. The Dragon then decided to live his life as a Human to the fullest, regaining his will to live. The Dragon was born into the child of a farmer who lives his live in the frontier. Even as a human, he possesses enormous amounts of power due to to his Dragon soul.

Original Webcomic:
http://www.alphapolis.co.jp/manga/viewOpening/333000127/