Billy is a resident living under the Arakawa River bridge, easily recognized by his appearance as a large, imposing man with the head of a cockatiel or parrot, often dressed in a sharp suit. He is a former member of the yakuza, specifically from a group known as the National Bird Association, and his past as a gangster is a core part of his identity. He left that life behind after falling in love with Jacqueline, who was the woman of his boss. This decision forced him to flee to the riverbed community to be with her.

In terms of personality, Billy projects an image of a rough and intimidating man. His speech can often carry a provocative or challenging tone, but this exterior hides a genuinely kind and caring nature. He is considered a man of deep honor and romance, capable of saying unexpectedly sweet and profound things, especially to Jacqueline. He commands a great deal of respect from the other residents, particularly from the character Riku, who is often moved to call him brother. Despite his intimidating presence, he is a "nice guy" whose gruff behavior is a form of expressing his unique kindness.

Billy's motivations are driven by his love for Jacqueline, for whom he sacrificed his former life and social standing. He is also motivated by a desire to live freely on his own terms, having rejected the rigid hierarchy of the yakuza world. His role in the story is that of a supporting character who, along with Jacqueline, represents the idea that the bridge is a refuge for people who have abandoned mainstream society for personal reasons. He and Jacqueline are one of the established couples in the series, and their dynamic offers a contrast to the developing relationship between the main characters. The community respects him, and his past connections sometimes bring elements of his old life into the narrative.

Key relationships are central to his character. His most important relationship is with Jacqueline, his lover, who dresses as a queen bee. Their bond is so strong that he left a powerful crime syndicate for her. He also has a connection with the boss of the National Bird Association, who was his former leader and whose wife he ran away with. Within the riverbed community, he is a respected figure and something of an elder brother or mentor figure to younger residents like Riku.

Billy does not undergo a dramatic personality shift, but his character is further explored and even comically deconstructed as the series progresses. He is shown to have fully embraced his identity as a bird, exhibiting behavioral traits like imprinting and the expectation to be fed regurgitated food by his partner. In a later storyline, he is captured by his former boss, who cuts off his wings as punishment. Following this traumatic event, he becomes more susceptible and is briefly brainwashed by the allure of comfortable luxury, such as a high-quality cage and delicious food, showing a vulnerable side that gets subtly broken over time.

His notable abilities are not combat-oriented but are tied to his physical presence and animal-like traits. He possesses immense charisma and a commanding aura, capable of inspiring admiration in other men without even trying. As a person who lives as a bird, he has peculiar avian habits, such as not eating anything other than raw vegetables that Jacqueline has chewed and fed to him. He is also physically resilient, having endured the loss of his wings. Despite these unusual traits, he remains a figure of quiet dignity and strength within the eccentric community.