moon

(1) [Muzan] had no human sensitivity and very little empathy. He had been a demon for a thousand years and had settled down, but when he was still human until the time he became a demon, he was so skilled at reading the negative emotions of others and spoke such abusive language to the point he drove five of his wives to suicide (in the Heian period).

On Demons

When Demons ingest human food, they just throw it back up.

Kibutsuji Muzan

He didn't need to sleep, and even though he had eternal life, he resented the restrictions on his daytime activities for a thousand years. He feared dying from sunlight, and to eliminate that fear he sought to be a complete person who can conquer death brought by the sun.

・Child form >> secured a place to make the medicine to overcome the sun.

・Geisha form >> gathered information on the blue spider lily and instructing humans to find it.

・Male form >> gathered information and secured funding for places where the geisha could not.

In some cases, he killed wealthy people and disguise himself as them to gather information and make money. If he ever sortied himself out, he made puppets out of his flesh and left it behind [his home/hideouts].

(2) Unlike ordinary Demons, Muzan could change his forms at will, from an adult to a small child, for a long time. His healing and regenerative powers were so much higher compared even to the Upper Moons, so he was able to nullify all of Tamayo's medicines as long as he had time.

Since the blue spider lily was hard to find, he sought to make the Upper Moons and those who have the constitution to overcome the sun at the same time. The doctor who used the blue spider lily [on him] lived in Tokyo, so he searched there in a frenzy, but turned up nothing.

(3) Depending on the climate, there were years when the blue spider lilies didn’t even bloom at all. Even when the flowers did bloom, it was only for a few minutes to less than an hour in the daytime, and then they closed back up. When they were closed, they looked like big horsetail weeds. Up until modern times, no one even knew they existed.

The sample withered under Inosuke’s descendant’s watch (it seems it was very difficult to get just the right water and soil quality, without which it will die), and they couldn’t raise new plants from its seeds, so it is thought that the blue spider lily is now extinct. It seems that the blue spider lilies left in the mountains also withered once the flowers around them were picked. Because they possessed some previously undiscovered components, researchers abroad who were planning to study them were also very critical [of the failure].

Since Muzan [who created demons] had also been defeated, there will henceforth be no new demons created.

T/N: Parts of this Muzan description is from this post and is reposted with permission from @demonslayedher.

Kokushibo

It seemed [Kokushibo] got along with Muzan well. The Demons were basically scared out of their wits that [Muzan] can read everything they were thinking, but Kokushibo didn't mind [the mind-reading]. He said he had no intention to betray Muzan, and felt better he didn't need to keep up appearances or hide his emotions.

[Kokushibo] never moved from being the Upper Moon One, and he was so happy when a favorite, Akaza, challenged him a death match to replace him, so he didn't consume [Akaza] and let the latter live (he usually absorbed [those challenging him] with Muzan's permission).

Including Akaza's, he was challenged to death matches to replace him in rank three times. Kokushibo's sword was made from his flesh and blood. Its name was Kyokokukamusari*.

*T/N: 「虚哭神去」, the closest of which I can translate as "hollow cry of the godless"(?), based on the kanji.

Doma

When [Doma] was 20 years old, he met Muzan and was turned into a Demon. He was so moved by his encounter with the latter he made Muzan the god of the Eternal Paradise Cult. Despite his loyalty and worship of Muzan, Muzan didn't like him.

It seemed in Muzan's experience, he had determined those without strong attachments or cravings wouldn't evolve greatly as Demons. Even so, [Doma] seemed to have more talent than the others, since he was able to rise up in ranks as Upper Moon Two.

He was sometimes consulted by his believers, and seeing them crumble under the weight of their desires, be it for money, status or love, seemed to be too foolish for him, but he felt curious what the feeling was like. He had money, status, and an almost-immortal body, but he didn't feel anything special, so he switched partners* every now and then to try to play the childish game of love.

*T/N: The word used actually is 「相手」, which is gender neutral, so it might be implied/inferred Douma might have been bisexual. Take that as you will.

Akaza

[Akaza] lost all [his] human memories when he became a Demon. Since the names of the techniques he used were important to him, it was likely that [deep down in his heart] he had people who he loved.

He felt no respect, no awe, no hatred, towards Muzan, and thought of [Muzan] as someone who gave orders and [of himself as] someone who obeyed. He couldn't bring himself to kill women, whether they be civilians or Demon Slayers. This was permitted by Muzan (who was sarcastic and constantly grilled people). Doma often complained about Akaza's special treatment.

He liked to talk to humans. Most of the time, even if it was someone he was going to kill, he would talk to them for a while, get to know them and then swing his fists at them. In the absence of Muzan's orders, he seemed to be doing nothing but working out.

He could share his thoughts and sight with Demons lower ranked than him (as much as Muzan allowed) and had complained to Muzan endlessly of Doma bothering him when the latter became Upper Moon Two. This was the only time he complained to Muzan.

Nakime

[Nakime] earned some money by playing the biwa, but she was a completely unknown [performer] and her husband always gambled, so she lived in poverty. One day, when her husband sold her only kimono for her biwa performances and used the money for gambling, Nakime became so angry, she beat him to death with a hammer.

After that she still had to work, so she performed wearing her tattered kimono, gaining disapproving looks from her audience, but when she played the biwa with strong and trembling hands, she was praised. From then on, she began to play biwa after killing people, and each time she did so, the sound of her biwa was highly commended.

She [randomly] chose Muzan [as a target] and tried to kill him but failed. However, he was so pleased with what she did, he turned her into a Demon.

Kaigaku

Kaigaku's sword was like Kokushibo's, and it was made out of his flesh and blood. Since he was still adamant on becoming a swordsman, it seemed like he made something resembling a nichirin sword.

Hantengu

[Hantengu] had been a liar since he was a child, and had a mind that twisted facts and interpretations to suit himself. He always thought he was the victim, and tried to make everyone around him look bad in order to gain sympathy.

Because he kept changing his name, age, and background quickly, he no longer knew his true name, age, or background. Several times, he married and had children but whenever accused of falsehoods and dishonesty, he would get upset he was mistreated and kill his wife and children, [and repeated the cycle all over].

He looked to be about eighty-seven years old. He believed that there was no one in this world more pitiful than himself.

Gyokko

Gyokko lived on the outskirts of a fishing village near the coast, and was disliked for repeatedly collecting fish carcasses and doing other strange things.

He lost his parents at an early age (they went out fishing and never came back, their drowned bodies found badly damaged), so the villagers kept their distance, thinking that he had lost his mind. However, Gyokko instead killed a village child who came to tease him and stuffed [the body] in a jar. It seemed he became fascinated by the beauty of his parents' drowned bodies [before].

In rage, the child's parents stabbed Gyokko with a two-pronged fishing fork. He was left to die there (a half-day passed and he was still alive) and Muzan was passing by, so he turned Gyokko into a Demon. His human name before then was Managi*.

When he became a Demon, he ate children's flesh and modified his body as he liked. Except for Muzan, he despised all living things, and he laughed and sneered at them from the bottom of his heart.

*T/N:「益魚儀」which means "benefit", "fish" and "ceremony" for their respective kanji.

Daki and Gyutaro

Until Daki's birth, Gyutaro lived in literal hell. Their mother, who was disgusted at Daki (due to her hair and eye colors, etc.) hated the baby and tried to strangle her to death, but Gyutaro saved [Daki]. He couldn't help but love her, she who cherished him, followed him and cried when he wasn't around.

On the day that their mother tried to violently cut Daki's hair with a razor, the balance of power between parent and child changed when Gyutaro became enraged and went on a rampage. Their mother got afraid of him and kept her distance from them.

Daki was so beautiful she could be approached just by walking down the street and given things if she smiled. Realizing this, she used this to make ends meet so she wouldn't be too hungry she couldn't stand up or feel like dying.

She had been nicknamed Shiraume-chan*. A reason why Daki gouged the samurai's eye was that he insulted Gyutaro.

*T/N:「白梅」means "white plum blossoms".

Enmu

Enmu's guts was actually eaten by a hungry Muzan and he was not supposed to be turned into a Demon at first, but as he felt no pain from the fatal wound, he envied and praised Muzan.

With those last words, his heart and brain stopped working, so Muzan turned him into a Demon. [Enmu knew] he was [converted] due to [Muzan's whim] and would only remember it in passing, so Enmu [did his best] to rise up to the ranks of Lower Moon One.

Rui

Although [Rui] had been a demon for less than twenty years, he was highly capable and was well liked by Muzan. In terms of ability, he was probably as skillful as the Lower Moon One or Two. He wasn't obsessed with numbers, so he didn't think about a death match to replace them. Muzan expected Rui would be able to defeat the Pillars.

If he recovered the power he shared with his individual "family members" before they were defeated one by one (he shared them his Blood Demon Art in the form of a spider they swallowed) he would have had a good fight with the Pillars, and might have been stronger than them.