Karl Akai is a detective who serves as the primary antagonist and manipulator in the narrative. Along with his partner, Kanye, Akai took in the young orphan Sawa after her parents were brutally murdered. However, this act of guardianship was a complete deception. Akai is in fact the one responsible for killing Sawa's parents, an act he committed to gain control over her and use her as a tool.

The character is defined by profound cruelty, hypocrisy, and a sadistic nature. Akai is portrayed as a pedophile who sexually abuses and exploits Sawa, effectively making her his sexual slave while acting as her legal guardian. His personality is marked by extreme manipulation; he lies to Sawa about the murder of her parents to ensure her obedience and wields his authority over her to break her will. A notable layer of his hypocrisy is that while he engages in the sexual exploitation of a child, he also secretly hunts down and kills other pedophiles, an act that does not stem from any moral code but rather from a twisted and illogical sense of personal preference or control.

Akai's primary motivation is to maintain power and control over Sawa for his own gratification and professional benefit. He and his partner train Sawa as a contract killer, using her to carry out assassinations on criminals and other individuals they believe have escaped justice. By holding the truth about her parents' death over her head and manipulating her emotions, he forces her to comply with his orders. His role in the story is that of a puppeteer, a corrupt authority figure who has transformed a traumatized child into a lethal weapon for his own ends.

His key relationship is, of course, with Sawa. This relationship is a toxic and abusive cycle of exploitation and violence, where Akai attempts to maintain total ownership over her mind and body. He also works in tandem with his partner, Kanye, who aids him in managing Sawa and their assassination operations. Akai's attempts at control extend to other characters, such as the young assassin Oburi; he employs Oburi while also secretly plotting to have him killed. Akai's development in the story is not one of redemption but of escalating cruelty and a desperate attempt to maintain his grip on Sawa. He ultimately meets his end when Sawa, having known the truth about her parents for some time, executes a long-planned revenge, ambushing and shooting him with his own weapons. As for notable abilities, Akai does not possess superhuman powers. His primary strengths lie in his cunning, his manipulative psychological tactics, and his position as a detective, which he uses to cover up his crimes and those of his protege.