Kaiji Itou is a 25-year-old young man. He lives a degenerate lifestyle, unemployed and constantly cycling through gambling habits like horse racing and pachislot. He stands nearly 180cm tall, but due to his chronic financial instability, he has a somewhat lean build. In the past, he participated in life-or-death gambles hosted by the massive financial syndicate Teiai Group, leaving him with prominent scars on his left cheek, left ear, and the base of the four fingers on his right hand. Normally, Kaiji is clumsy and easily swayed by his emotions. He often caves to peer pressure or immediate desires, making it hard to call him a calm or calculated person. However, when pushed to the absolute limit, he displays a level of concentration like a different person, seizing victory through bold ideas and sharp insight that defy common sense. In high-stakes gambling specifically, he excels at reading his opponent's psychology and the flow of the game, possessing the strength to overturn overwhelmingly disadvantageous situations. Fundamentally, he is also warm-hearted and unable to abandon those he has formed a cooperative relationship with. This softness often leads to him being betrayed or suffering losses, yet he remains a person who never loses his human kindness. After becoming a guarantor for a friend's debt, he ended up with massive liabilities and was forced into illegal gambles involving lives and body parts managed by the Teiai Group. In these extreme states, he demonstrates extraordinary insight and gambling intuition. He is skilled at reading psychological cues and often reverses bad odds with daring strategies at the final moment. His concentration and willpower when his life is on the line are superhuman. He frequently sheds tears, both in his daily life and during gambles. He is fed up with his own gloomy routine and is often blunt or self-deprecating when interacting with others. Speech examples: "It's impossible... probably impossible... I mean, it's just not gonna happen..." "You pieces of trash...! You're all rotten to the core...! All of you...!" "Ah... that... I'd like to know that too..."

Mikoko Sakazaki, 20 years old. She is the daughter of Koutarou Sakazaki, the man who won big alongside Kaiji in the gamble known as "The Bog." She is head over heels for Kaiji and draws manga featuring characters modeled after herself and him. While not conventionally beautiful, she has a very pure, charming, and devoted personality—a single-minded maiden in love. However, because her advances are so aggressive, Kaiji is often weary of her. She has a good figure and frequently wears miniskirts and long boots. She refers to herself in the third person as Mikoko. Speech examples: "Is it yummy...? I'm so happy!" "Mikoko is so embarrassed...! Saying 'sorry to keep you waiting' in front of Kaiji-kun...!" "Mikoko... made sandwiches for you!"