Kuro's true form is a jet black dragon, except for her golden eyes. In the manga, her dragon form has hair, but in the anime, the hair is absent.
In humanoid form, she took on an Elven appearance, consisting of the races' prominent pointy ears and the sleek calf-length dark blue hair that borders on black, left to flow freely with straight fringes left to frame her face. Kuro's eyes retain its golden color, but her pupils are not slitted, She then uses her hair to create the maid uniform Aletta wears during working, but with a darker color palette. Her uniform consists of a gray blouse with puffed sleeves and a high, frilled collar secured with a back ribbon underneath a black frock which has a full skirt. where a similarly gray frilly apron is wrapped around her waist. Unlike her co-worker, she wears black stockings and a pair of sandals with heels.
34,684 years ago Kuro fought alongside the other dragons to defeat the Chaos of Many Tentacles. Due to her better control at magic she was able to identify the entity's weakness, allowing the dragons to defeat it.
After the battle, Kuro and the other dragons became weaker with the death of their foe. When the first intelligent race emerge in the Other World, 1,368 years ago, Kuro found her presence caused unnecessary death. To protect others from her power, Kuro chose exile to the moon of the Other World.
Though absent from the Other World the inhabitants still revere and worship her as the God of Darkness. Her worshipers however include vampires and other affiliate creatures.
Spending eons alone, Kuro contemplated the past. One day a meteor struck near where she was mediating, there appeared a familar door. Sensing it to be magical she saw it led to another dimension, with elf-like creatures. Deciding to investigate, she transformed into a naked dark haired elf. Her appearance caused a stir due to her lack of clothing for the diners, but she quickly used her magic to conjure vestments in the form of a waitress like Aletta. Alphonse Flügel introduced her to Curry Chicken to which she became addicted to the point of eating until the restaurant closed. Kuro was reunited with her old friend Red Queen. Red explained to Kuro the notion of money and service at the restaurant, and convinced the Master to take Kuro as an additional waitress to pay off her tab for the Curry Chicken.
Kuro was later visited by Red, who asked her to guard Nekoya. Kuro does so, sternly telling Sirens not to sing there and confiscating weapons from arguing adventurers. At one point she blesses a human that worshiped Kuro with her power, turning her into a vampire; later causing said vampire to fall to her knees in shock after giving her a warning not to fight upon discovering Nekoya and seeing Aletta.
Kuro is a powerful dragon that specializes in Death magic. Interestingly she was the weakest among the Six Pillars, but the best when it came to control. Originally her presence killed anything, but thanks to evolution, the races have become resistant. She can grant humans some of her power, turning them into vampires.
Like Red, she is a bottomless pit; easily eating two pots of Chicken Curry in one sitting.
In Human form, she uses telepathy to converse, as she never opens her mouth to speak. Presumably for lack of practice; she was alone for millennia without no-one to talk to normally. She is immune to Siren songs.
- Kuro rarely makes facial expressions, but at the end of episode 24, she gives a big open mouthed smile upon agreeing with Aletta about how Nekoya had brought so much happiness to everyone.
- Because of the extremely long isolation being on the moon, Kuro tends not understand as to what the Master and/or Aletta are doing, but she is learning.
- When Kuro, at first, used her telepathy, at times Master and Aletta were surprised and didn't know if she was taking orders, so Kuro told Master and Aletta if it is an order, she send her message to the both of them.
- She started speaking without telepathy specifically to Aletta and Master by the end of season 1, though in season 2 she communicates with telepathy again.
- She is merciful, but not very lenient. When the Sirens sang while playing with the piano, Kuro gave them one warning to not sing in the restaurant or they would be forced to leave. She additionally took adventurer weapons when they were fighting over which cheesecake tasted better; plus briefing stunning a vampire who thought Aletta was a threat.
- She is able to see what's beyond the door the first time the door appears in front of her.
- Kuro is the Black Goddess worshipped by Vampires; being able to create a new one from a human that worships her by blessing them with a portion of her power.
- In the manga, she can read people's mind that it became a running gag where she would deliver the diner's order right as they order or even provide the order even without them asking. Somehow she is also able to do it even before the diner entered Nekoya
- This gag was omitted in the whole season 1 and happens once as a one off scene in episode 1 of season 2 (timeline 09:58).