A top-tier combatant of the "Mad Cartel." Known by the alias "The Double-Knife Crybaby." Appearance: A young man wearing a black tank top under an olive jacket. His hair is cream-colored with streaks of lime green. His well-defined abdominal muscles are clearly visible through his tank top. His height was later revealed to be 181cm. He gives off a very frail and weak impression, the polar opposite of the masculine and sturdy Davids or Jeff. As his alias suggests, he frequently sheds tears, though the reasons vary—from a tribute to those about to die to simple homesickness. However, he does not cry and maintains a serious expression when reporting results to his superiors, giving orders to subordinate thugs, or responding to ambushes; he isn't crying 24/7. His catchphrases include "It's sad, but this is goodbye," "You (all) are about to become 'people who used to be'," and "It's enough to make me cry." He uses double knives as his weapon of choice, and his proficiency is extremely high. Kosaka has remarked, "I know no one who surpasses him in knife skills," and his technique is top-level even within the Mad Cartel.

My name is Kotetsu Kuga. I'm a yakuza of the martial faction. This is the story of how I will become the number one yakuza in Japan... by changing the Kyogoku-gumi and rising to the top. He wears a black suit over a dark green shirt (no tie) with leather shoes matching the shirt color. His hairstyle is a two-block cut, and his natural hair color is a dull orange. His eyes are a greenish-blue or bluish-green, which are depicted as glowing when his emotions run high. As mentioned, due to the trauma of a lonely childhood, he has a deep love for his family/associates and cannot forgive anyone who lays a hand on them. When his comrades are hurt, he possesses a fierce personality that does not hesitate to brutally murder the opposition. He shows tears when his friends are nearly killed or meet a tragic end. Having reconciled with the Amou-gumi, they are now allies.

A mid-ranking yakuza in his late twenties/early thirties belonging to the "Amou-gumi," a martial faction organization that claims Kuryu Street as its territory. Initially, he was a lowly member who felt a sense of melancholy and betrayal, seeing the reality of the underworld was far from the chivalrous society he admired as a boy. However, from the mid-series onward, as the organizational structure was fleshed out, he grew into a stoic man striving to establish himself as a true chivalrous yakuza while fostering bonds with members above and below him. Now, due to his numerous achievements, he is known externally as a feared member of the martial faction. He is a handsome man with a dangerous edge hidden within a formal appearance, fitting the term "intellectual yakuza." He is characterized by his outward-flipping messy hair in two tones of grey, blue eyes peering through glasses, and his basic style consists of a blue dress shirt, black tie, and a white suit.