To activate the Akuma, the Millenium Earl finds people destroyed by despair of the loss of a loved one. He offers them a way out of their misery, a chance to see their loved ones again. All they need to do is summon the soul of the dearly departed and place it in the Akuma by simply calling out the loved one's name with all their heart.
What the Earl won't say (until it's too late) that once the soul enters the Akuma body, the soul now belongs to the Earl and would obey him unconditionally. The active Akuma will then take the life and 'body' of the one who summoned them. Now it can pass off as a normal human in society, to spread more death and despair for the benefit of the Earl and his plans.
Like any organism, the Akuma undergoes several stages of metamorphosis as it grows. However, both the process and result are wicked.
This is the Akuma, Level 1. This is its true form initially after activation, a large metal pod that can float and fly with a number of cannon barrels protruding out of its body. These cannons fire bullets made of hardened Akuma blood which carries a virus that gives instantenous cellular death to any normal living human organism, human or animal.
Akumas of this level are impervious to conventional human weapons since being made of 'dark matter.' Only weapons made of 'Innocence' (white matter) can destroy these nightmares easily.
Later on, the Exorcists encounter these type of Akumas I call, "modified Level 1s".
Unlike the original Level 1, these do not need to transform into floating pods. Any surface of their bodies can immediately twist and transform into gun or cannon barrels to fire their deadly blood bullets. But again, they do not exhibit more power and can be easily defeated by Innocence weapons.
That's all for now for Akuma Level 1. I'll discuss the other Akuma types in future posts
