The leader of Scar Chain, a group of Deadmen that oppose the the prison and plan to leak the truth to the rest of the world. Nagi speaks with a mechanical voice created by a synthesizer because of his vocal chords being removed after a rigged fight with his lover, who was later killed by Genkaku of the Undertakers. He has a son, left in the care of a nursery outside, and fights for freedom to see his child. His branch of sin is called "Owl's Eyeball", which creates small floating explosive spheres that can be controlled and detonated remotely. It was later revealed that Nagi's son actually died in his mother's womb when Nagi's wife was killed. This prompted Nagi to develop a second, horrifyingly savage and inhuman personality, which slaughtered numerous Undertakers in vengeance. Genkaku is especially fascinated by this and later drugs Nagi to bring to light this side of him, which causes Nagi to temporarily revert to his second personality and attacks his own comrades. Ganta manages to bring Nagi back to his senses, but then, Genkaku fatally wounds Nagi by blasting a hole in his stomach, as he claims that he loves Nagi's dark side and will kill Nagi to bring him salvation, if he chooses to stay the person he is. However, Nagi still manages to stop Genkaku from dodging Ganta's powerful attack, which permanently incapacitates Genkaku, and dies shortly afterwards.
A kleptomaniac and an informant to Assistant Warden Tamaki, You was hired to watch over Ganta in return for large amounts of Cast Points. Though apparently friendly and polite, in truth he is ruthless, scheming and somewhat paranoid, given his position as a spy for the prison's staff. A rarity among the prison population, You got himself captured and sent to Deadman Wonderland in hopes to find his sister Minatsuki and buy her freedom with the accumulated Cast Points he got from Tamaki. He cares deeply about her, so much so that he is often thought of suffering from a sister complex, much to Minatsuki's disgust. The two eventually manage to forge an estranged relationship. (Source: Wikipedia)
Fujiyoshi is a Deadman and a former member of Scar Chain. He died during the Deadman mass prison break. In the anime, he was named Matayoshi instead of Fujiyoshi.
Mitsuzaki Yosuga is a Deadman previously captured at Deadman Wonderland. After it fell, she joined Makina's expedition and return to DW to permanently destroy it and the Wretched Egg. She tells that she's Sakigami Toto's big sister, and part of the reason she agrees to return to DW is to find out what happened to her brother. Later, a flashback shows that they aren't actual siblings. Yosuga is an orphan brought into DW by Tamaki, and Toto's family (including his older sister) had already died. It's implied that Toto claimed Yosuga as his older sister due to Yosuga's resemblance to her, although Yosuga is younger than Toto. As time went on, she started to think of Toto as her real brother.
A member of Scar Chain, a group of Deadmen that oppose the prison and plan to leak the truth to the rest of the world. Karako loves its leader, Nagi, deeply and fights to help him achieve his dream of freeing the Deadmen. She is able to use her Branch of Sin to wrap blood around her body to increase her physical strength while using the Wushu martial art style or defend herself. She can also close up wounds using this technique. She wears a little bell as a necklace. She used to be a nurse before her time in DW.
A mysterious Deadman feared even by Senji, Toto is a mysterious boy dressed in a way reminiscent of Shiro, and appears not only to be one of the strongest Deadmen introduced so far, but also to know in great detail about the true nature and purpose of Deadman Wonderland. His power, Love Labyrinth, allows him to copy the abilities of other Deadmen. However, he states that he recently was reset of his copied powers after his battle with the Red Man. However, even in his weakened state, he managed to take down two of the Forgeries with nothing but a copy of Crow's powers. Nicknamed Mockingbird, he freely comes and goes through the prison, and recently has become friends with Ganta. Toto is the only person to have fought the Red Man and have survived. He's later revealed to be the chief of Deadman Wonderland and true main antagonist, Hagire Rinichirou. By using the combined ability of his two bodyguard, "Hollow Swallow", Hagire was able to transfer his mind to Toto's body and took over it. What happened to Toto's personality is currently unknown. It's assumed that he is on the protagonists side, as he alerts Shiro about the data chip, and takes out Hibana with Invisible Black.