The story takes place between episode 22 and episode 23 of Blue Dragon: Tenkai no Shichi Ryuu. Shu, Bouquet, Marumaro and Noi travel to the floating city of Flugel, to gather more clues regarding the Investiture Beings. There they meet the city's guardian Jiranda and the priest Eba where they find it inhabited by robots only.

(Source: Blue Dragon Wiki, edited)