Senji was the first "Deadman" that Ganta encountered at the prison. After making their way to sector G, Crow destroyed the Necro Macro security robot which had been chasing Ganta, Shiro and Yoh. After a small skirmish, and an interruption by Shiro, Crow was subdued by the Deadman security. The next day, Ganta and Senji were slated to be the next two Deadmen to compete in the "Carnival Corpse." Despite Senji's experience and skill with his 'branch' ability, Ganta managed to win by fooling Senji. As a consequence for losing, Senji's right eye was removed for research. He returns a short time later during Ganta's next match, sporting an eyepatch and gives Ganta assistance with figuring out his opponent's techniques. He also helps Ganta understand his own capabilities. His change in personality toward Ganta is due to his respect for Ganta's strength. Senji comments that because Ganta beat him, he is not allowed to lose until they have a rematch. He seems to thoroughly enjoy violence, and his favorite phrase is "Dead Center" (or in the dub of the anime, "Sssslice."). Despite his wild and battle-hungry attitude, he does have a sense of honor and respects strength and determination. In an ironic twist, Senji becomes flustered and embarrassed when a woman acts immodest. When he first notices Shiro's form fitting body tights, his face becomes red and he give her his coat telling her to quickly cover up. His Branch of Sin is called "Crow Claw". It manifests as two large scythe-like blades, made of blood, extending from long cuts on his forearms. He makes these cuts using two bladed rings he wears on his thumbs. While the blades are typically two to three feet long, Senji has demonstrated the ability to greatly lengthen them allowing him to attack people at range. He is responsible for naming Ganta's 'Branch of Sin' (Ganta Gun). He also has a supersonic attack called Invisible Black. Senji used to be a policeman before his time in DW. It's hinted that he killed four friends.
It's revealed in his fight with a Forgery that Senji did not kill them, but was indirectly responsible for their deaths. After the Tokyo massive earthquake, chaos ruled in Seiji's inspection area, and out of the corrupt police force, only Seiji and his friends were active against the local crimes. Their actions soon drew hostile attentions of many hoodlums, especially to Seiji since the branch of sin he possessed was a powerful asset. They challenged Seiji to a many-on-one battle, but his friends stopped him and took on the offer, and ended up savagely murdered in his place. As such, he partially believes Ganta in that he did not kill his friends, because he has experienced similar circumstances