Barbatos is Lord Diavolo's loyal servant. Barbatos has short dark green hair with bangs reaching his eyebrows. The fringe on his left is longer, reaching his nose and has a turquoise ombre. Like all the other demons, Barbatos has painted fingernails. Barbatos's nails are a mauve purple color. Barbatos has a very calm demeanor, although he does enjoy lightly teasing other people. He is nice towards MC and often saves leftover sweets he bakes for them. Barbatos takes his position as a butler very seriously. He even teaches the demon brothers intricacies about his job in the Demon de Butler event. The demon brothers believe that Barbatos could do anything, thus resulting in them frequently seeking out his help. While typically exuding a calm demeanor, Barbatos seems impartial to being interrupted when speaking about something he is passionate about, According to Little D. No. 2, Barbatos's smile remains in place even when he is angry. Some of the other demons think that Barbatos is shady and scary. Some are convinced that Barbatos has a hidden room in the Demon Lord's Castle where he partakes in the act of torturing people

Diavolo has layered, red hair with his bangs parted to the left side, tan/dark skin (depending on his form), and pale golden eyes. Like the brothers, he too has painted nails - black, in his case. Despite being one of the most powerful demons in the Devildom as well as the Future King, Diavolo takes on a surprisingly fair and compassionate, if not joyous, attitude at almost all times. However, that is not to say he is a soft or lenient ruler, as even without the threat of retribution from Lucifer, all demons appear respectfully intimidated by him. Diavolo proves to have much more wisdom than his cheerful demeanor suggests. He shows moments of solemn clarity in which he correctly predicts events that will occur in the future either due to his subtle encouragement or his intentional lack of intervention. He has the ability to tell if someone is telling the truth and has made a rule for himself to never tell a lie. The goals that Diavolo sets for himself, his fellow demons, and the three worlds at large, appear to be pursued with the utmost best intentions. This is evidenced by the fact that so far he has only ever done what he believes is best, with the desire to improve the lives of those he rules over, even if the process is painful