Diablo/Relationships

Rimuru Tempest
Diablo is fanatically loyal to Rimuru worshiping him like a god. He will follow Rimuru's orders and commands to the absolute letter. Nothing makes Diablo happier than carrying out his master's will; he will become saddened should he need to be away from Rimuru from extended periods, but will follow his task quickly as possible to facilitate a swift return. Diablo follows Rimuru in the belief that the "truth" of the world will reveal itself to his master, whom overcame many obstacles and achieved great power while uncovering secrets lost to time.

Shion
They are rivals for being the "primary" secretary for Rimuru, aside from that they both share a similar fanaticism for Rimuru, though for different reasons. Shion taught Diablo to always considered any possible request Rimuru may ask; so he may be ready on the spot.

Benimaru

Diablo and Benimaru seem to be on friendly terms with each other. They fought in the last round of the Tempest Tournament; Diablo came in second, as he couldn't go full power without killing Benimaru.

Souei

Diablo and Souei seem to be on friendly terms with each other. As the leader of Temlest's information network, Diablo trusts Souei to keep their mastee up to date on the goings-on with other nations.

Hakurou

Diablo and Hakurou seem to be on friendly terms with each other.

Goblin/Hobgoblins
Rigurd

Diablo and Rigurd seem to be on friendly terms with each other.

Rigur

Diablo and Rigur seem to be on friendly terms with each other.

Gobta

Diablo and Gobta seem to be on friendly terms with each other; despite Gobta's moments of idiocy, Diablo recognizes his combat skill.

Framea

Diablo was tasked with watching the rabbit beastman during her her stay as a guidebook creator for Tempest; he noted her to be quickly endeared to the residents. Per Rimuru's order, Diablo tested Framea's combat ability; believing her to be adequate. Later, after hearing of the horrifying time she endured from trying to be Carrera, Ultima and Testarossa's guide on their day off, Diablo planned to discipline the trio on Rimuru's order.

Humans
Shizue Izawa

Diablo respected Shizue Izawa as a Wreathy Hero and opponent when they battled each other. He even saved her life from the demons he was contacted to hunt down and kill.

Black Demons
As a Primordial, "Noir" has numerous demons that are descendent from him. Due to Diablo's (Noir) unique personality and loner tendencies however, its been stated that demons belonging to his linage is few when compared to the number of demons created by the other primordials, this was due to Diablo himself having stated to dislike creating demons and preferred to operate on his own.

Regardless of this, its been stated by many that the Demons descendent from him have more or less taken after his unique personality and preference for individualism.

Greater Demon Subordinates
Due to his dislike for working in large groups, Diablo, while he was still unnamed, only had two other Greater Demons as his subordinates. The two of them were shown to have been very loyal to him and stayed by his side and assisted him in whatever he needed. Later, the extent of their loyalty to Diablo was fully shown when the two had no hesitation to sacrifice themselves to Rimuru on Diablo's command to complete his transformation into a Demon Lord.

Guy Crimson
They are old friends who often fought and competed with each other. They were once similar in power but Diablo stopped pursuing strength.

Black Numbers
Diablo's faction of subordinates, numbering several hundred. As a show of loyalty to Rimuru, Diablo returned to the underworld to recruit only the best of the demons to serve Rimuru. This included the Violet, White, and Yellow progenitors. They were named and allowed at least one lieutenant each. From this group, Diablo has Venom serving as his lieutenant.