Mina Hiraya is a supporting character in Sword Gai: The Animation. She is a member of the Bureau of Historical Management, an organization that deals with cursed weapons. Hiraya holds a nurse qualification and works as a counselor, skills that serve her mission-oriented role within the bureau.

Her primary assignment involves Naoki Miki, whom she is assigned to as his counselor. To maintain close observation, she enters into a fabricated romantic relationship with Miki, effectively posing as his lover while carrying out her duties. When she determines that Miki has become terminal—likely meaning he is beyond recovery or poses a threat—she deceives him without hesitation and proceeds to carry out his disposal. This demonstrates her calculated nature and unwavering commitment to her mission above personal attachments.

Hiraya is portrayed as a young woman with white skin, brown eyes, and brown hair. Her personality is marked by a cold pragmatism; she is able to separate emotion from duty and act decisively in the interests of her organization. She is defined by her loyalty to the Bureau of Historical Management and her willingness to sacrifice personal relationships for the greater objective of containing cursed weapons.

Her key relationship is with Naoki Miki, her former fake lover and eventual target. While presented as an ex-girlfriend, their connection is entirely manufactured for her assignment. She does not undergo significant personal development within the story; rather, she serves as a symbol of the bureau's ruthless efficiency. Her notable abilities include her medical training, psychological counseling expertise, and her capacity for deception and cold decision-making under pressure.