Cecil von Gielen, one of the twin sisters alongside Karin von Gielen, captured Sara Scorpion to compel her cooperation in wielding the legendary Bernstein Sword. The twins obtained this sword ten years prior by killing Sara's family and destroying her city. Cecil possesses black hair, red eyes, and typically wears her hair with a white puff accessory on the right side. Her attire features a lilac tone, contrasting with Karin's dark blue clothing.

She constantly carries a teddy bear concealing an arsenal including a machine pistol and hand grenades. In close combat, she employs a lightsaber distinguished by its blue, wavy blade. Cecil exhibits pronounced sadism, displaying childlike playfulness while taking extreme pleasure in tormenting and humiliating prisoners such as Sara and Sylia.

Despite her noble lineage as part of the Gielen family, Cecil engages in aristocratic conflicts, specifically targeting the nobility. The twins' actions against Sara are driven by their ambition to control the Bernstein Sword, an artifact believed to guarantee galactic dominion.