Eight years before the events of Deadman Wonderland, in 2016, Kiyomasa Senji was an 18-year-old police officer assigned to Tokyo in the aftermath of the Great Tokyo Earthquake. Alongside his colleagues Akira Shindō, Tōshirō Kan, Momoi, and his mentor Domon, he was tasked with restoring order to the devastated city. Even at that time, Senji possessed his Branch of Sin, which he frequently used to subdue criminals, earning him a reputation as a ruthless yet effective enforcer of justice.

An anime-exclusive episode expands on Senji’s time in the police force. During one of his missions, he chased down and cornered a thug, brutally attacking him with his Crow Claw. Seeing the criminal as nothing more than scum, Senji prepared to kill him but was stopped by Domon, who reminded him of the line between law enforcement and vigilante justice.

Later, at the police station, tensions arose when Senji was accused of tipping off a suspect, due to his past associations with street thugs. The accusation led to a violent altercation with his colleagues. Frustrated, Senji took a walk through a local market, where he spotted a boy named Izuru being pursued by members of the Goreless Peace gang for stealing from them. Senji intervened, beating up the gang members and escorting Izuru back to the orphanage where he and his sister Hinata lived, unaware that the gang was following him.

As Senji returned home, he was confronted by Keigo Ugachi, the gang’s leader, who attempted to recruit him. When Senji refused, Keigo retaliated by attacking the orphanage, massacring Izuru, Hinata, and the other children inside. Enraged, Senji and his comrades launched an assault on Keigo’s hideout. Domon and his team stormed the compound, taking down gang members, while Senji pursued Keigo, who trapped him using his Wire Lyre Branch of Sin. Senji struggled to break free but was ensnared again.

Domon arrived to aid Senji, but Keigo mortally wounded him. In a fit of rage, Senji extended his Crow Claw, stabbing Keigo through the chest. As Keigo begged Senji to finish him off, Senji was more than willing, but Domon intervened, warning him that killing Keigo would make him no different from the criminals he fought against. At the last second, Senji hesitated upon seeing Keigo flinch in fear. Overcome by exhaustion, he passed out, and Keigo was arrested and later imprisoned in Deadman Wonderland.

Due to the police squad’s effectiveness, numerous criminals sought revenge against them. A coalition of gang members formed under the leadership of Ikazuchi Akatsuki, targeting Senji and his team. Despite Senji’s insistence on fighting alongside them, his comrades went ahead without him, fearing for his safety. When Senji finally arrived, he discovered that his entire squad had been brutally murdered, with the sole exception of Domon, who was fatally wounded.

Before dying, Domon imparted a final lesson to Senji, reminding him that relying on others is not a weakness, but rather an essential part of life. His last words to Senji were: “If depending on others is a specialty of kids, then acting all cool is a specialty of adults.”

Following these traumatic events, Senji was eventually apprehended and sent to Deadman Wonderland. As a tribute to his fallen comrades, he had their initials DSMK tattooed above his right eye.

Four years before the series’ events, Senji became infamous within the prison after a Necro Macro, a deadly security robot, was deployed to subdue him when he went on a rampage. While the machine successfully captured him, it resulted in the deaths of twenty-four other prisoners in the process. This incident cemented Senji’s status as a legendary figure among Deadman Wonderland’s inmates, feared and respected for his unparalleled combat prowess.

Kiyomasa Senji is a tall, muscular man with a tanned complexion, giving him a strong and imposing presence. He wears his short black hair spiked back and has the letters DSMK tattooed above his right eye as a tribute to his fallen police comrades. His intense expression and battle-hardened physique reflect his years of combat experience, both as a police officer and as an inmate in Deadman Wonderland.

During his time as a police officer, Senji wore the standard police uniform, maintaining a disciplined and professional look. However, after being imprisoned in Deadman Wonderland, he initially wore the standard orange prisoner uniform before later adopting a more distinct outfit in G Ward. This consisted of dark blue pants with a black belt, a sleeveless tank top, leather shoes, and a long black coat, emphasizing his rough and rebellious nature. He also carries two rings with serrated blades on his thumbs, which he uses to slice open his forearms to activate his Branch of Sin, Crow Claw.

Following his Carnival Corpse match against Ganta Igarashi, Senji suffered the loss of his right eye as part of the Penalty Game and now wears a black eyepatch over it. At one point, when attempting to reintegrate into society, he wore a business suit and neatly styled his hair, presenting a more refined and controlled appearance, though this was a stark contrast to his usual rugged look. Later, after his battle with Hagire, he sustained another severe injury, resulting in the loss of his right arm below the bicep. Despite these physical changes, Senji’s formidable presence remains, marking him as a resilient and battle-tested warrior.

Senji is a fierce and battle-hungry individual who thrives in combat, often expressing his enjoyment of violence through his signature phrase, “Dead Center” (translated as “On target” in Tokyopop’s version, “Bang” in the manga scanlations, and “Ssslice” in anime fansubs; ズッパシ, zuppashi in the original Japanese). His aggressive and relentless fighting style reflects his unwavering confidence in his abilities, and he rarely backs down from a challenge. However, despite his wild nature, Senji adheres to a strong sense of honor and deeply respects strength, perseverance, and determination.

This sense of respect is evident in his interactions with Ganta Igarashi, whom he initially overpowers in their Carnival Corpse battle. However, after witnessing Ganta’s refusal to surrender despite overwhelming odds, Senji decides to mentor him, teaching him various techniques to wield his Branch of Sin more effectively. His belief in strength is not just limited to physical prowess but also includes emotional resilience, as seen when he advises Ganta to understand Shiro’s predicament before making any rash decisions.

Despite his affinity for combat, Senji does not believe in needless killing. This is demonstrated during his first encounter with Ganta, where he chooses to spare him after noticing that Ganta made no effort to fight back. While ruthless toward opponents in battle, he is capable of kindness and can be considerate toward those he respects.

In an ironic contrast to his rough exterior, Senji becomes easily flustered in situations involving immodest behavior from women. When he first notices Shiro’s form-fitting bodysuit, he turns red with embarrassment and hurriedly hands her his coat, urging her to cover up. Similarly, when Minatsuki Takami flashes her underwear at him, he reacts in a similarly awkward manner, even collapsing from shock in some instances. These moments highlight a humorous and unexpectedly bashful side to his otherwise intense and hardened personality.

Rings
Senji is equipped with a pair of specialized rings designed to help him activate his Branch of Sin, Crow Claw. These rings contain rotating serrated blades, which he wears on both of his thumbs to cut his forearms and draw blood for his attacks. The rings are a crucial part of his combat style, allowing him to use his abilities with precision. However, after losing half of his right arm during his battle with Hagire, he ceased wearing them, as he could no longer use them effectively.

Coin
Senji possesses a one-sided coin with a salamander insignia on both sides, a keepsake left to him by his former mentor, Domon. This coin holds great sentimental value, serving as a reminder of his deceased sensei and the lessons he imparted. Senji cleverly uses the coin to boost Ganta Igarashi’s confidence, winning bets by always calling heads, knowing that the coin is rigged. Eventually, as a symbol of trust and encouragement, Senji gives the coin to Ganta, passing on a piece of his mentor’s wisdom.