the Akuma are the minions and personal army of the millennium Earl and Noah's family. Despite their name (Akuma is the Japanese word for Devil) their aren't infernal demons or anything else, but weapons which are build by the Earl, using the soul of a dead human and the body of one alive. The Akuma are programmed for killing humans and fight against the exorcists who are the only persons who can defeated them with the help of the innocence, which is in contrast with the Dark Matter that compose their body. Despite they act like villains and seems cruel and merciless in killing humans, they are make with suffering humans souls, who are enslave to the Millenium Earl's commands, and forced to obey to him against their will.
Creation and purification
The Akuma are create when the Millenium Earl make a contract with a person who lost a loved one, promising to him/her to bring back his/her soul from the after life, but this is only a trick. In fact when the soul of the dead is summon by the Earl, it is trapped in a Dark Matter Skeleton, and forced to obey to the Millenium Earl who orders to the new Akuma to kill the person who asked for his/her resurrection, and take control of his/her body. After their birth,Akuma continue to live between humans, hiding their presence and pretending to be like them for kill in secrets the people, evolving themselves and become more powerful.
The only thing who can destroy the Akuma is the innocence, which is use by the exorcists in their fight against them. If the akuma is kill by an exorcist, the soul in the inner can find peace and rest, but if the Dark Matter explode or is destroyed in other ways, the human soul vanish forever.
Level 1 consists of a floating ball shaped creature with dozens of gun barrels protruding from it that fire large bullets. The gun barrels are flexible and can be bent to face any desired angle without affecting its firing capabilities.Level 1 Akuma appear to be able to fire beams of energy from an opening beneath their face. This attack is called "Akuma Cannon" by the Earl. The souls inside a Level 1 Akuma have the bodies and clothes of their original forms. However, their faces are rather distorted and there is a chain around their necks expressing the intense pain and sadness of the trapped soul. Level 1 Akuma exhibit something of a transition from the deterioration of their human personality into an evil personality for level 2 later on as observed in their increasing obsession to simply kill and may, hence, show zombie like behavior in their human form. A Level 1 Akuma will advance to a Level 2 once it has fulfilled a substantial quota of kills of humans and exorcists.
Level 2 is the second evolution stage of the akuma, when a level 1 kills a sufficient number of humans or exorcists, increasing the power of the Dark Matter. The level 2 has big differences from the previous level, as the advancement of a personality and a one's own dependence ( but they are still loyal to the Millenium Earl and to the members of Noah's family).The souls of Level 2 Akuma seem to become more deteriorated. There many types of Level 2, and they can have many different appearances and powers. There is not a common appearance for the level 2, but in the anime and manga appears many Akuma with the features of gas, fire, dolls, a demonic court jester, even a playing card, and they especially take form of animals.They also have different powers, such as copying a person's appearance (mirror image), emitting "ice fire" which hurts worse than normal fire, creating blades of air, emitting destructive sound waves, and creating bubbles that absorb water from everything they touch. Some Level 2 Akuma even carry modern day weaponry such as homing missiles and various types of firearms that resemble machine guns and so on, as observed in the manga, and they can also have the commands of big groups of level 1. After murdering enough people, it can evolve to Level 3.
The level 3 was considered the most powerful and terrifying stage of the Akuma (before the unexpected birth of the level 4) by the black order and the exorcists. all level 3 Akuma become bipedal, roughly 8 to 9 feet tall, with sharp jagged teeth, and wear what looks like medieval armor that covers most of their bodies. the difference between each other is the form and the colour of their armors. A Level 3 Akuma is easily capable of standing up to multiple Exorcists in combat and usually has an extremely powerful ability in addition to its greatly improved strength and speed. like their previously stage, the level 3 seems to have a specific ability, but until now only two powers have been shown, like create gravitational chains and the crumblings of the atoms.They have also been shown to cannibalize their fellow Akuma. Their abilities seem to revolve around the use of Dark Matter, the polar opposite of Innocence. The souls embedded in the Level 3 Akuma are near gone and appear as a floating dark mass with eyes.