Gascogne Rheingau serves as the head of the Registry system aboard the battleship Nirvana. Her primary responsibility is managing the supply of weapons and equipment for the Dread fighters, ensuring they are properly armed for battles against the Harvesters. She carries out these duties both from within the ship and by piloting a delivery vessel to provide direct support during combat. Her role extends to being the third-in-command of the Nirvana, ranking directly after B.C. and under Captain Magno Vivan.

In terms of personality, Gascogne is a steady and grounding presence among the crew. While her subordinates in the Registry department may become flustered or overwhelmed by the intensity of battle, she remains composed and encourages them to keep their cool with her characteristic phrase "Smile, smile!" She often takes on the role of a big sister to the rest of the crew, offering advice that is frequently sarcastic but well-intentioned, even if not always appreciated by its recipients. Her relationship with the protagonist Hibiki Tokai is notably close; she spends her free time playing poker with him and acts as a guiding figure, providing him with counsel throughout their journey. She has a particular aversion to being called by the nickname "Gasco".

Gascogne's motivations are rooted in supporting her crew and maintaining the operational integrity of the Nirvana. She is dedicated to her work and to the safety of her comrades, demonstrating a willingness to put herself in harm's way for their sake. This is most evident during a critical battle in the Second Stage against a Harvester mothership. When Barnette’s Dread fighter is threatened by a Copy-Nirvana, Gascogne pilots her delivery ship into the fray and launches missiles at the attacking unit, successfully jarring Barnette loose. The Copy-Nirvana then turns its focus on her, impaling her ship. As the vessel crashes into the mothership and is engulfed in flames, she is presumed to have perished.

Despite this apparent sacrifice, Gascogne survives the ordeal. She reappears during the final battle against Earth, piloting the very Harvester mothership that had seemingly destroyed her, having commandeered its systems for her own use. This return speaks to her resourcefulness and resilience. While not a frontline Dread pilot herself, her notable ability lies in her logistical coordination and the calm, efficient management of the Nirvana's arsenal, which is vital to the ship's combat effectiveness. A small but meaningful personal item she carries is a metal straw that she keeps in her mouth; when crushed in her hand, it bends into a key, and this object is a keepsake from her sister.