Black Numbers

Black Corps is a unit of Tempest composed solely of elite demons that serves Rimuru under the leadership of Diablo.

They are approximately 700 personnel consisting of Diablo's old rivals, their subordinates and unique individuals. After being summoned, these demons are made to inhabit/possess the demon dolls inside capsules developed by Tempest.

Black Corps is consist of
 * 600 Nameless Greater Demon (some of them evolve into Nameless Arch Demon).
 * 100 Nameless Demon Chevalier
 * 2 Named Demon Baron
 * 2 Named Demon Viscount
 * 1 Named Demon Count
 * 1 Named Demon Marquiss
 * 1 Named Demon Duke
 * 4 Named Devil Lord

Background
It was an idea formed from the mind of Diablo, whom planned to form a force worthy of serving his master, Rimuru. Thus Diablo set off to the Underworld to search for potential demon candidates, laying waste to countless demons in his wake.

After gathering the suitable candidates, Diablo presented them to Rimuru upon his return to Tempest and summoned ten elite demons that he deemed worthy.

Known members
The Black Numbers: 700 personnel consisting of Diablo's old rivals and their subordinates and unique individuals
 * Diablo (Leader and Founder)

The Devil Lords trio names:
 * Testarossa
 * Ultima
 * Carrera

The Demon Nobles' names:
 * Venom
 * Veyron
 * Moss
 * Shien
 * Zonda
 * Agera
 * Esprit

History/Growth
Among them, there are originally 3 Arch Demons, 7 Greater Demons and the remaing are Lesser Demons.

The 3 Arch Demons evolve into Demon Dukes after being named then were further evolved into True Demon Lords/Devil Lords when granted the 100,000 souls from Rimuru. These are the names of the Devil Lords trio: Testarossa, Ultima, Carrera. Simultaneously as they are named, the incarnation and evolution process was completed, they leave their capsules as Demon Dukes and all three of them are beauties.Their might is horrifyingly overwhelming while their strength is on a completely different dimension.

The 7 Greater Demons evolve into Arch Demons after being named. Upon the evolution of their masters, the Arch Demons evolved into Demon Nobles. The Demons Nobles have a name for each of them: Venom, Veyron, Moss, Shien, Zonda, Agera, Esprit.

Their evolution completed in an instant after they're named, and emerged from their cultivation capsule. They have the strength of Arch Demons as the obvious fact.

The souls of Lesser Demons are also just right for inhabiting the demon dolls. After inhabiting those dolls, they have the strengths of Greater Demons despite being Lesser Demons

Dozens of these Lesser Demons, who become Greater-demons-like, have abilities above A ranks. Among them, if there's someone with a unique ability, they might even evolve into strong Arch Demons even if they're weak.

100 Greater Demons were born among the total of 700 Lesser Demons' souls that are lodged onto the cultivated demon dolls due to accumulating enough magic essence/energy for evolution from inhabiting the dolls. These demons are revealed to be powerful with abilities that surpass the Majins/Devils.

The 100 Greater Demons evolved into Demon Chevaliers (Knights) and the 600 Lesser Demons evolved into Greater Demons when their Masters evolved into Demon Lords.

Trivia

 * It's Implied that Black Corps have enough power to Overwhelm and Conquer The Eastern Empires. (Excluding Velgrind)
 * The Black Corps is The Strongest unit in Tempest.
 * The Black Corps have the Fewest Members in Tempest.