Three brothers make a promise. A Promise to become the world's strongest and open Heaven's Gate. They who were trained by the most legendary man in the history of the world, must fall and live in the Mortal Realm in hopes to save the world from destruction... The story follows Albus, a shameless boy with a cloud spirit. After traveling to the Mortal Realm he meets a young girl. And from there he ends up following the footsteps of the man who raised him without knowing.