Principal Dio Eraclea is the sixteen-year-old younger brother of the most powerful Guild member, Maestro Delphine Eraclea. People see him as a rare find that will someday take over the Guild. He is very playful and fearless, and treats many things like they were games. His odd nature can be seen in his awe of Claus Valca's skills and giving him the nickname "Immelmann" (referring to the World War I German ace, Max Immelmann and the maneuver Claus frequently used while flying, the Immelmann turn). This strange nature is mostly due to the Guild lifestyle and fear of his sister Delphine. His first appearance in the series is marked by a chess-match with his beloved friend Lucciola and with the Guild's power and surveillance, watches the skies of a skirmish between Guild ships searching for Alvis Hamilton and the Silvana. He finds extraordinary talent in Claus's vanship piloting, and after the Horizon Cave Eight vanship race, he starts to have strong interactions with the main characters. He later joins them on the Silvana in order to escape his sister. Though his initial presence with the Silvana was unwanted, his participations and interactions with Claus and Alvis eventually earn the entire crew's trust, and is acknowledged as one of them, during a birthday party proposed by Alvis. He is forced back to the Guild during the end of the series, and is brainwashed by a Guild device in preparation for the "Rite of the Covenant".