Hakkou is a character of striking and memorable appearance, known for her long, wavy mint-green hair that reaches her waist, often tied back with a ribbon. She has matching lime-green eyes and a tall, curvaceous figure. Her typical attire consists of a long-sleeved white blouse and a long, dark olive-green skirt, though she also wears a revealing cat costume while working at a cosplay bar in Shanghai.

Originally from a village in the Middle East, Hakkou is a carrier of the Ua virus, a condition that manifests as a distinctive pattern on her body and grants her a lethal special ability. She is a profoundly quiet individual, communicating almost exclusively through nods and head shakes, as she is seemingly incapable of speech. This silence is not born of shyness but is a necessary restraint; her voice is a weapon that inflicts severe mental interference on anyone who hears it, capable of causing brain damage or even death.

Despite her deadly potential, Hakkou possesses a kind and gentle nature, often behaving in a childlike manner. Her motivations are simple and revolve entirely around her lover, a man named Santana. She works diligently in his establishment and shares a home with him, her entire existence seemingly dedicated to their relationship. She is intensely protective of him, and her life gains purpose through her devotion.

Within the narrative, Hakkou serves as a poignant figure representing the tragic consequences of the Ua virus. Her role is largely defined by her relationship with Santana and her interactions with other characters who come to her place of work. A key relationship is, of course, with Santana himself, for whom she harbors deep, albeit unspoken, feelings of love. She is also connected to the other Ua virus carriers and finds herself caught in the conflicts that surround them.

Hakkou's tragic development culminates when she is tricked into speaking, which inadvertently causes Santana's death. Overcome with grief and despair, she drags his body away and ultimately chooses to die alongside him, remaining with his corpse as the world around her collapses. In her final moments, she helps another character find a cure for the Ua virus, providing a single, selfless act of good before her end.

Her notable ability is her voice, which functions as an uncontrollable and devastating psychic attack. The sound waves from her speech directly affect the brains of those nearby, causing intense pain and rapidly proving fatal if she speaks at length. This power makes her a tragic figure, unable to communicate in the most basic human way without becoming a danger to everyone around her, especially the person she loves most.