Nameless Worm

Nameless Worm are the parasitic worms that enhabit the bodies of the Deadmen.

History
The worms were originally created by Sorae Igarashi and Hagire Rinichirō. Together, they researched different ways of heightening a person's immune abilities. The pair used several guinea pigs including Shiro for these experiments. Their existence was determined to be a byproduct of the pair's research.

Due to the Great Tokyo Earthquake, the worms were spread throughout Tokyo.

Effects of the Worms
Main Article (Deadmen)

Once inside a human, the Nameless Worm integrates with the body, altering the subject permanently. When this happens, the person is then refered to as a Deadman.

Most Deadmen were infected during the Great Tokyo Earthquake, however, there are exceptions, namely Ganta Igarashi, who was infected by the Wretched Egg, during the Nagano School Massacre.

Powers
Main Article (Branch of Sin)

The Branch of Sin (罪の枝, Tsumi no Eda) is the ability to control and freely move your own blood outside of the body. The Branch of Sin is mostly used as a weapon and can be formed into various objects. People who have a Branch of Sin are known as Deadmen. This power was created by the Nameless Worm carried by the Red Diamond. To summon their power, they first need to inflict at least a minor cut in order to draw the blood out of their body. While using this ability, the users blood is directly linked to their arteries and can be restored if it's still connected to them. In very few cases, the user can fully control his blood while its not directly linked to them and even reuse the blood to recreate their weapon. In a case where a Deadman sustains deep wounds or cuts, they can slow down their blood or stop it at certain parts of the body to prevent it from bleeding out. Different Deadmen have different powers. It's unclear if Branches of Sin manifest a unique power on their own or if they adapt to the Deadmen's genetic and biological characteristics. Whatever the case may be, all of Deadmen have been known to master their powers with enough amount of training. The Branches can be long range, close range or both. Long range Branches can either be thrown, shot, or extended to reach their opponents at a certain distance, while close range Branches are bound to close quarters combat. Deadmen can use more blood in order to enforce their Branches ability, as well as increasing their size or lengthening them if needed. The two main disadvantages to this power are anemia and Worm Eaters. Anemia is mostly common to the ones who use long range Branches, although many Deadmen have been known to overcome it over time, either from their training or because of the Nameless Worm itself that altered their bodies.

Certain Branches of Sin have been developed far enough to achieve the speed of sound by breaking the sound barrier. This ability increases the speed of one's own power, enabling it to cut or pierce through enemies and solid objects, as well as easily overpowering Worm Eaters. Despite the lack in power, it uses less blood, preventing Deadmen from falling victim to anemia. The only Deadmen to achieve this are Ganta and Senji canonically and Minatsuki  and Hagire  (While possesing Toto's body) exclusively to the anime. To achieve the speed of sound, different methods are applied to each Branch, as Ganta makes his bullet smaller and slimier, focusing more power into the blast and Senji, who makes his blade thinner and draws it in less than one second.

It was shown that Branches of Sin can evolve over time, such as Ganta's Ganbare gun and Senji's unnamed evolved Crow Claw. The evolution itself has occurred due to their strong will to live and high determination, eventually leading to their new powers. Evolved versions don't stray too far from their original powers and appearance, as they only intend to boost them with speed and strength. Patterned, black lines (shiny red-pink in the anime) appear on Deadmen when using the evolved Branch of Sin, usually from parts of their body where they manifest their Branch of Sin, all the way to their face, or in Wretched Egg's case on her entire body, when her full power awakened. Their appearance is distinct for every Deadman, from straight patters, to curly lines. The main disadvantage to this ability is that it uses a lot of blood and puts strain on the body. Overusing it will cause third degree burns and scars where the marks appear, all the way to the location of the red crystal inside the Deadmen's body.

Synthetic Copies
Main Article (Forgery)

Tsunenaga Tamaki was able create artifical Deadmen called Forgeries. They posess the powers of Deadman as well as a poison (carried in their Branch of Sin) designed to give them an advantage over Deadmen. The copies are forced to wear masks that not only induce brainwashing effects, but cause the wearer to remain in a heightened, euphoric state.

Their elite troops are called Complete Forgeries.

Removal
Main Article (Worm Eater)

Worm Eater is a device that instantly oxidizes the Nameless Worm residing in the Branch of Sin. With the Nameless Worm gone, a Deadman's blood becomes useless, making him unable to attack.

The Worm Eater was invented by Tsunenaga Tamaki and was given to the Undertakers. It has been effective against every Branch of Sin, except for the ones that evolved, such as Ganta's Ganbare Gun and the original Branch of Sin of the Wretched Egg.

The only way to counter a Worm Eater with a regular Branch of Sin is to attack with the speed of sound, breaking the sound barrier, like Senji's Invisible Black and Ganta's Supersonic Ganta Gun.