David Steinberg, known online by the player character name Kusame, is a figure who operates on both sides of the digital divide in the world of.hack//The Movie. He is an agent of the NAB, the Network Analysis Bureau, a global investigative service that handles cyber-crimes and anomalies. His primary responsibility in the film is to investigate a series of strange and dangerous phenomena occurring within the online game The World. He is specifically assigned to look into the matter of a special item known as the experience cube, which has been entrusted to a young player named Sora.

In his physical form, David is an adult male, estimated to be in his mid-to-late thirties. He is a professional who works alongside a partner named Eleanor, though his past holds a hint of having lived in Japan before his overseas assignment with the NAB. His personality is defined by a calm, methodical dedication to his duty as an investigator. He does not simply observe from a distance; he takes direct, measured action to intervene and guide the course of events. This is most evident when he personally approaches Sora in the real world, not as an ominous authority figure, but as an informant. He explains to her the reason she was chosen by the ultimate artificial intelligence Aura to safeguard the cube and, more critically, explains why she must ultimately return it. This interaction reveals a man who is patient and understands the weight of the digital crisis, acting as a bridge of information between the bewildered user and the unseen forces of the network.

His role in the story shifts dramatically when he logs into The World as his alter-ego, Kusame. This player character is a far cry from an ordinary avatar. Kusame is a mysterious, cheat-type PC described as a human-beast hybrid, bearing a distinct visual resemblance to the Egyptian deity Anubis. In terms of gameplay class, Kusame functions as a Wavemaster, a magic-oriented class that specializes in support and spellcasting. However, his true significance is not in standard combat but in a single, pivotal ability. During the final confrontation against a massive Virus Bug threatening to consume the game, Kusame intervenes at a critical moment. He demonstrates the power to freeze all of the game’s in-game time for a duration of thirty seconds. This temporal stasis creates a narrow window of opportunity for Sora, allowing her to safely navigate a deadly path and reach the abode of Aura, ultimately saving the system.

Key relationships drive his actions and his development. His partnership with Eleanor is central; they are coworkers who trust each other within the high-stakes environment of cyber-investigation. His relationship with Sora is more transactional yet crucial; he acts as a mysterious benefactor and guide, providing her with the truth she needs to complete her quest. While his primary motivation is to resolve the digital anomaly and secure the Origin containing Aura to protect the network, his story does not end with the film's credits. In a continuation of his narrative, he secures this Origin onto a chip, becoming its sole guardian. This act of protection plunges him into a violent, real-world conflict where he is betrayed by his own partner, Eleanor, and hunted by an eco-terrorist group. In these events, his development from a bureaucratic investigator into a desperate, resourceful survivor is stark. Despite suffering severe wounds, he displays a tactical ingenuity, using decoys, prosthetics, and sheer will to eliminate his pursuers. In his final act of sacrifice, he uses a prosthetic arm to eject the precious data chip from his own left eye, hiding it before collapsing from his injuries, seemingly accepting death to ensure the data's safety.