Her physical features are very similar to that of her "Younger Brother," Rui. She has a completely pale, milky-white skin complexion with snow white hair and her eyes are pure white with only her silvery pupils separating them from her sclera. She also possesses several red, dot-like patterns on her face similar to her "family". Her original appearance as a demon was completely different than her current, having morphed and changed her features due to being forced by Rui as a condition to be accepted into his family. Her original appearance was simpler, having black hair and slitted cat-like eyes and pale grayish skin.
The Older Sister Spider Demon is shown to be the most cautious within her "family," having instead opted to observe and stand back rather than jump right into the battle against Demon Slayers. She is also shown to be one of the most cowardly of her family, both with battling against the Demon Slayer Corps and dealing with her family's internal conflict. When her "Mother" was being violently abused and reprimanded by her "Younger Brother" and her "Father," she stood back and gave her "Mother" the same severe glare due to her weakness instead of helping her. She again shows her cowardice by trying to convince Rui to run instead to fight after most of their family was defeated.
In truth, the Older Sister Spider Demon loathes and hates her "family" and had begun thinking that she would have likely done better on her own. She believes that the rest of her family are idiots for playing along with Rui, despite him not having any real emotional attachment or care for any of them. She nonetheless did whatever it took to survive and stayed with them, knowing she stood no chance of surviving if she were to try to escape. She even went as far as attempting to use sympathy and pity on Shinobu Kocho, knowing that she was a demon slayer, by pleading that she was forced into her situation by Rui. However, this contradicts her actions as she went through various lengths to stay with him and his family, revealing that she only does what is convenient for her own survival. She later shows herself to be gullible enough to fall for Shinobu's fake sympathy and begin to openly admit her total count of human victims.
Originally, the Older Sister Spider Demon was a lone demon who decided to team up with Rui's group on Natagumo Mountain in order to survive out of fear of the Demon Slayers. Rui forced his new "family" to abandon their previous appearances and faces in order to match his. The Older Sister Spider Demon was compelled to be his "Older Sister" and protect him using her own life, due to his belief that the older sibling should always shield the younger sibling. She and her family then began preying on the native humans from around the mountain, which brought about the attention of the Demon Slayer Corps and led to them sending scores of their Demon Slayers in an attempt to rid the mountain of the demons. The Older Sister Spider Demon herself managed to kill at least 80 or so humans during her time on the mountain. She successfully stored them inside her thread sacks using her Blood Demon Art for later meals which were soon found by Shinobu.
Shinobu suddenly appears behind the Older Sister Spider Demon, inquiring if the strings came out of her palms, wishing the creature a good evening, and commenting on the beauty of the moon that night. Startled, the Demon attacks the Demon Slayer with her strings, but Shinobu dodges them all effortlessly. Drawing her sword, Shinobu dryly comments that this attack means the Demon doesn't want to get along with her.
The elder sister Demon quickly begs Shinobu for mercy, stating that she would be killed if she disobeyed Rui. Shinobu, sympathizing with the creature's plight, says that she will cooperate with the Demon if she answers a few of Shinobu's questions, the first of which being how many people she had killed. The Demon's answer is five, but Shinobu assures her that she doesn't have to lie, complimenting her string technique from earlier, and the Demon corrects her answer to eighty humans. Despite the creature's stubborn denial, the female swordsman notes that both of them came from the west side of the mountain, and, on that side, she had found forty of the Demon's cocoons. Shinobu adds that she isn't angry, only trying to be as accurate as possible. When asked what the point of checking this information is, Shinobu tells the elder sister Demon that in order for them to be friends and to satisfy those who have died, she will have to endure punishment, explaining in gruesome detail what she had in mind for this, and adding that the creature won't die from it, so there will be no aftereffects.
Enraged, the Demon attacks Shinobu again, but the female Demon Hunter quickly bypasses her, simultaneously landing her "Caprice" attack on the creature. She laments the Demon's poor choice, turning and subsequently watching as the creature collapses. Shinobu tells the creature not to let her guard down just because she can't cut the Demon's head off since, she explains, she utilizes poison as her weapon instead. Shinobu then introduces herself as the Insect Pillar of the Demon Slayer Corps, stating that, although she may be the only one among her order to not possess the ability to cut off a Demon's head, poison that can kill the creatures is still a potent tool. She then apologizes, realizing that the elder sister Demon is already dead and couldn't hear her explanation.
Abilities and Powers
- Regeneration - The Older Sister Spider Demon displayed decent enough regenerative abilities to immediately and easily reattach and heal her body after being violently torn to shreds and decapitated by Rui during his fit of rage.
- Shape-shifting - The Older Sister Spider Demon appeared to have enough skill and talent in shape-shifting in order to alter her physical appearance to match Rui's in order to fulfill his desire for a family. However, if frightened or startled, her physical appearance returns to its original form, showing that she needs to keep conscious effort to maintain her new physical characteristics.
- Acid Cocoon (
溶 解の 繭Yōkai no mayu?) - The technique works by entangling her target in a web-cocoon filled with acidic fluids which are capable of dissolving the clothes of the victim (even the specially made battle uniforms of the Demon Slayer Corps). The acid will then move on to the target's flesh, making their body soft and ready for her to consume.
There were non-manga additions added to the Older Sister Spider Demon’s backstory in the anime. In the manga, there were more than five members of the spider family, although it was implied
that they were killed prior to the arc. Such additions are:
- Showing how she joined the family and how the family members were treated by Rui and each other.
- Showed more of the Spider Demon Family outside of the main five.
- Her interactions with another 'older sister spider demon', who, after befriending, proposes that they run away together when Rui isn't around. The Older Sister Spider Demon ends up betraying her to Rui in order to gain his favor and the other Older Sister gets beaten and hung up to be killed by sunlight.
- In the manga, the four members join up before meeting Rui; in the anime they joined Rui before the Older Sister ever met him.