Nine Violet, codenamed Twin Phantom, serves the clandestine organization Black Fund alongside her twin sister under their adoptive father, Black Trader. She possesses pale skin, stands 158 cm tall, weighs 43 kg, and has short green hair featuring distinctive V-shaped bangs over her blue eyes. Her demeanor is characteristically quiet, taciturn, and expressionless, speaking rarely. Despite this reserve, she harbors a kind heart and displays a notable affinity for animals, often seeking their company in natural settings.

Orphaned young when arson claimed their parents, Nine and Tesla were adopted by Black Trader. He manipulated them into believing the Twin Angels caused their parents' deaths, forging their initial antagonism towards Haruka Minazuki (Red Angel) and Aoi Kannazuki (Blue Angel). This deception drove them to operate as Twin Phantom, opposing the Twin Angels' missions.

In combat, Nine transforms into Twin Phantom, specializing in close-quarters physical assaults. She wields a large greatsword to deliver powerful, overwhelming strikes, contrasting Tesla's long-range lightning abilities. Her transformed attire includes underboobs as a distinctive feature.

A pivotal revelation occurs when Nine and Tesla uncover Black Trader's lies about their parents' deaths and his true motives. This truth shatters their allegiance to Black Fund, leading them to reconcile with the Twin Angels. During this transition, Nine gradually forms a bond with Haruka, initially unaware of her identity as Red Angel. Post-reconciliation, the sisters become allies, joining forces with the Twin Angels and Kurumi Hazuki (White Angel) to combat Black Fund remnants and other threats. Nine evolves into a supportive combatant within the group, contributing her swordsmanship to their collaborative efforts.

Her story concludes with integration into St. Cherine Academy's daily life and continued heroic activities. She maintains her reserved yet compassionate personality while actively participating in the team's missions.