Bandō is a former operative of the National Police Agency's Special Assault Team (SAT), an elite tactical unit. In his mid-thirties, he is a fully human soldier who stands out even among his highly trained peers for his exceptional combat skills, determination, and an aggressive, almost sociopathic demeanor. His personality is defined by a profound bloodlust and a deep-seated need for a challenging fight, viewing violence not just as a duty but as a personal pleasure. He is highly apathetic, anti-social, and arrogant, showing little regard for authority or the safety of others, including his own colleagues.

Bandō is introduced as an antagonist sent to recapture Lucy following her escape from a research facility. His initial encounter with her is catastrophic; after provoking the emergence of her murderous personality, he is easily overpowered. Lucy severs his right arm, shatters his left forearm, and destroys his eyes with her invisible vectors, leaving him blind and bleeding on a beach. This humiliating defeat becomes the sole driving force of his existence, transforming his lust for battle into an all-consuming obsession for revenge against Lucy.

Following his maiming, Bandō learns he has been infected with the Diclonius virus, meaning any children he fathers would be born as Diclonii, and he is slated for forced castration. He violently rejects this fate, escaping from the hospital before the operation can be performed. To prepare for his rematch with Lucy, he undergoes surgery to receive advanced biomechanical implants, including bionic eyes and a powerful myoelectric prosthetic hand. He also acquires custom.50 caliber handguns, whose immense power can pierce through a Diclonius's otherwise impenetrable vector defenses at close range. His strategy becomes one of meticulous preparation, such as clearing a beach of all debris to deny Lucy any ammunition to throw at him.

Despite his brutal exterior, Bandō possesses a complex, hidden side that emerges primarily through his interactions with others. He forms a significant bond with Mayu, a runaway girl who saved his life after his first defeat. He shows her a grudging, protective compassion, even giving her his contact information in case of trouble. This reluctant kindness extends to Nana, a gentle Diclonius, and Kurama, the scientist who once hunted him, whom he saves from suicide. While he remains violent and crude, he operates by a personal code of honor and expresses intense disgust at acts of perversion or child abuse, as demonstrated when he brutally rescues Mayu and Nana from a predatory assassin.

Bandō's role in the story evolves from a one-dimensional human antagonist to a more complex anti-hero figure. His primary motivation remains fixed on killing Lucy, but this quest forces him into unlikely alliances and reveals his capacity for self-sacrifice. In a pivotal moment, he shields Mayu from a fatal attack by Lucy, an act that results in his body being cut in half. As he seemingly dies in Mayu's arms, he confesses he had always wanted someone to mourn for him, a wish he had suppressed his entire life by isolating himself from others. His story concludes with his unexpected survival, as he later returns with his lower body replaced by bionics, suggesting his obsessive will to live and fight is nearly unbreakable. In the anime adaptation, his character development is significantly reduced, and he does not receive the same level of depth or a definitive conclusion.