Neviril is the Sibylla Aurea and the regina, or leader, of Chor Tempest, one of the choirs of priestesses who pilot the advanced airships known as Simoun. She is widely regarded as the best Auriga, or pilot, in the entire Simoun fleet and is deeply admired by both her fellow sibyllae and the cadets aboard the Arcus Prima. Her skill and reputation are such that junior sibyllae are reprimanded for addressing her without an honorific even in her absence. Neviril is the daughter of Halconf, the chief administrator of Simulacrum's government, which gives her a privileged background within the theocratic nation.

Neviril enrolled as a sibylla around the age of seven alongside her best friend Paraietta. She quickly demonstrated exceptional talent in flying, and her leadership abilities became highly coveted as she matured. She formed a romantic and piloting partnership with Amuria, and together they became known as the best Simoun Sibylla duo in existence. However, early in the war between Simulacrum and Argentum, Neviril and Amuria attempted a dangerous and powerful maneuver called the Emerald Ri Mājon. Neviril hesitated after making eye contact with the enemy, causing the maneuver to fail. The resulting explosion killed Amuria, leaving Neviril devastated and unable to pilot for a period.

After Amuria's death, Neviril was removed from active piloting and fell into deep grief and despair. Her personality, once charismatic, refined, and polite, became clouded by sorrow. She struggled to accept a new partner until the arrival of Aer, a new sibylla with unwavering morale. Despite Aer's persistent attempts to partner with her, Neviril remained too trapped in her loss. Eventually, through continued battles and a pivotal event where a suicide bomber sabotaged peace talks, Neviril began to emerge from her depression and accepted Aer as her partner. Over time, she fell in love with Aer, though she was initially haunted by memories of Amuria.

Neviril's role in the story is central. As the leader of Chor Tempest, she must guide her team through war while grappling with her own trauma. Her key relationships include her late partner Amuria, who shaped her early identity; her childhood friend Paraietta; her father Halconf, who takes a keen interest in her career; and ultimately Aer, whose persistence helps her heal. Neviril's development is marked by a journey from grief and isolation to renewed purpose and love. She learns to move forward despite loss and eventually chooses to fight for a new future.

Notable abilities include her exceptional piloting skills as an Auriga, which make her the most revered pilot in the fleet. She is also capable of leading and inspiring her choir, and she possesses the knowledge and courage to perform the powerful Emerald Ri Mājon, a maneuver that allows time travel. In the final events of the story, Neviril and Aer together pilot the Ventus Simoun and successfully perform the Emerald Ri Mājon, vanishing in a flash of light to march toward a new world together.