Mother was very similar in appearance to her "son" Rui, having the same milky-white skin, teal eyelashes and nails, and circular, red facial markings. She also possesses a short and curvaceous physique. Additionally, she had bushy eyebrows and long, white hair parted down the middle of her face which was tied with teal orbs into two, thick strands.
Mother wore a lengthy, layered kimono — maroon on the inside layer and white on the outside layer — that exposed part of her chest and was tied with a patterned obi. She also donned a beaded necklace composed of teal and purple orbs and decorative anklets. She also goes barefoot and has black nail polish on her toenails; the lower front of the kimono is open, exposing her legs.
However, it was revealed that this was not her true appearance, as her body was altered to look like Rui's. Her original appearance was completely different from her transformed one, with a much smaller, childlike body compared to her new, more voluptuous figure. Her skin was marked with two maroon lines on each of her cheeks and her eyes were rounder with yellow irises and x-shaped pupils. She also wore her short, black hair parted to the side with bangs framing her face and two, low pigtails.
Like most Demons, Mother is cruel, unfeeling, and murderous towards humans. She ruthless controlled dozens of Demon Slayers through her threads and manipulated them into killing each other. She was also rather sadistic and callous, uncaring that her manipulation brought them agony and leaving them alive in intense pain. In spite of this, spending time with Rui's family caused her developed an intense fear for him and Father, both whom had abused her for being weaker than expected. This abuse was severe enough to cause her to fully embrace death instead of having to continue on knowing that both Rui and Father would continue to torment her.
In her final moments, she seemed to have regained some of her feelings and memories as a human and seemed to have been genuinely touched by Tanjiro's kindness, thanking him for giving peace by warning him that a Twelve Demon Moon was on the mountain, wishing him to be careful in her last moments.
It was later revealed that compared to the rest of her "family", she was technically the youngest demon of the family (her original appearance being that of a young girl) and was still coping with her previous human feelings and memories, which made her to cry and grieve many times when remembering them. Due to this she became a target of severe reprimand from Rui, due to her inability to be a proper "Mother" to her "Children", who were all technically older than her.
Not much is known about Mother's past as a human, but she was loved and cherished by someone, a young female person with a maroon haori and black hair styled in a low cut bang with a ponytail. In her final moments, she seems to have remembered some parts of her life as a human child such as remembering being loved and cherished by this person.
After she became a Demon and lost her loved one (the implication is that they somehow died in a rather bloody manner), she took up residence at Mount Natagumo. Later, Rui came to Mount Natagumo, convinced her to join him, and then forced her and her soon-to-be family to transform themselves to look like him and become his "family". She was given the role as the mother of this family, but because of her being a very young demon, she was unfit for the role and was met with chastise and abuse from both Rui and Father.
Rui assigns Mother with the role to protect Mount Natagumo and her 'family' from the Demon Slayer Corps. Sitting atop a rock in the middle of a clearing, she defends the mountain via numerous threads strewn across the forest. Sensing that Demon Slayers were sent to kill her family, Mother used small spiders to attach her threads to them. With their bodies in her control, she manipulated the Demon Slayers into killing each other, later keeping their bodies attached to use as dolls for fighting against more intruders.
Tanjiro and Inosuke enter the mountain in order to defeat her and her family. They were met by the sole survivor of the initial massacre, Murata, who informed them of what happened. Soon after, she sends her numerous dolls to kill the trio, but their simple movements were easily evaded. They learned to slice the threads to free them from controll and avoid the spiders sent by her, allowing Murata to hold them off as Tanjiro and Inosuke ventured further into the forest.
As they got closer to her, Mother's threads become harder and her dolls, some of whom were still alive, became stronger. She is confronted by Rui, who asks if she can win and why she is taking so long. Due to her fear of him, she initially doesn't answer, too afraid to say a response. Rui then threatens to inform Father about the situation if she does not kill the remaining Demon Slayers quickly, which causes Mother to fearfully say she can win. Now in a state of panic, Mother resorts to using the rest of her dolls and pushing them even harder to kill Tanjiro and Inosuke. The two eventually get closer and encounter her last dolls, including a young girl named Ozaki and another Demon Slayer in agony over his broken body. Mother pushes their bodies to the limit to kill Tanjiro, breaking Ozaki's arm and continuing to attack the Demon Slayers.
However, Tanjiro is able to entangle the threads of Ozaki and her comrades by launches them into the tree branches and leaving them hanging by the threads. With Inosuke's help, they disable all of the dolls without killing them. Angered at their failure, Mother resorts to using her strongest doll instead and kills her human dolls by snapping their necks. Enraged, Tanjiro and Inosuke continue through the forest to find her, unknowingly coming across her final doll, a giant headless demon with bladed arms. Though the doll proves much faster and stronger than the controlled Demon Slayers, Tanjiro and Inosuke are able to coordinate a plan together and kill her final doll.
As she panics upon learning her last weapon was defeated, Mother looks up to see Tanjiro descending to kill her. In shock of her impending death, she suddenly realizes she can be freed from her abuse and surrenders to him, releasing her threads in a final act of embracing death.
Having already given up any form of resistance and willpower to continue fighting, Mother holds her arms up awaiting death from Tanjiro's coming attack. Tanjiro, realizing that she no longer has any intention of fighting back, finishes her with the Water Breathing: Fifth Form - Blessed Rain after the Drought instead of the First Form: Water Surface Slash as originally intended. He instead opts to use a form that brings no pain after seeing her no longer willing to fight back.
After she is beheaded, Mother is shocked at how peaceful and painless her death is and is even further surprised and touched by Tanjiro's eyes, which has no malice, hate, or contempt. Instead she sees nothing but pure kindness and mercy. As she fades away she remembers all the painful memories and unkind stares her family had given her and vaguely recalls her past as a human, remembering being loved and cherished by someone and as she slowly disintegrates into ash, weakly wondering where that person is now. In return for Tanjiro's kindness, she weakly warns him that one of the Twelve Kizuki is in the mountain and bids him good luck as she dies.
Shapeshifting: The Mother Spider Demon has shown advanced skills in the shape shifting, as she managed to change and alter her skin color, hair length and color, facial structure, demon marks, eye color and physical characteristics to match and resembles Rui's own physical features and maintain these changes for extended periods of time. However, most likely due to her young age as a demon, she would sometimes accidentally revert back into her true form - much to Rui's annoyance, making him severely punish her.
Puppetry: The Mother Spider Demon can create and manifest threads from the tips of her fingers that can extend to cover an entire mountain. She uses her threads in a unique manner; by utilizing them to manipulate bodies like puppets. She does this by attaching her strings to her intended victims using small spiders, allowing her to control them from a remote distance. She can even use these strings to somehow bring out the full physical power of her controlled puppet to its maximum, albeit at the cost of putting her puppets through severe physical pain due to it. This ability also allows her to control the corpses of Demons, as she somehow acquired and preserved the dead body of a demon and prevented it from disintegrating to black smoke for use in combat. The closer the strings connected to her are, the more power she can exert over the puppets she manipulates.
Spider Manipulation: The Mother Spider Demon can create and command small white spiders with red dot like design similar to the physical traits of herself and her "family" to stealthily attach her threads to her intended victims without them noticing. These spiders also have similar traits to demons, as they burn up upon getting stabbed/sliced by a Nichirin Sword.
- Mother Spider Demon was ranked in 34th place as of the first character popularity poll with 32 votes.
- Both of the Mother Spider Demon's voice actors share the role of Beidou from Genshin Impact.
- (To herself about Tanjiro Kamado) "Those eyes.... Such kind eyes... Back when I was human, I think someone used to look at me with kind eyes. I wonder who that was. I can't remember. It was someone who always treasured me. I wonder how that person is doing now."
- Kimetsu no Yaiba Anime: Episode 16.