Spider Family

The Spider Family was a clan of Spider Demons, formed and led by the Lower Moon Five, Rui of the Twelve Demon Moons.

Profile
The clan was a group of five Demons, the Father Spider Demon, Mother Spider Demon, Older Sister Spider Demon, Older Brother Spider Demon, and finally Rui,who portrayed himself as the youngest brother of the family, but in actuality was the true leader of the group. However there where likely more members initially as the Older Sister noted that there where indeed more demons located in Natagumo Mountain, but were all disposed of by Rui when they refused to play along with his given "Family" roles and where punished by having their intelligence removed and where then strung up in the trees until morning came and where burnt to death by the sun.

The Spider Family was an oddity, as Demons typically don't form groups. Although calling themselves a "family", the clan was highly dysfunctional at best, and downright violent and sadistic at worst within their own kin, with torturous levels of physical and psychological abuse being commonly practiced. There was no real love or trust between its members at all, as Tanjiro put it, it was a fake that reeked of mistrust, fear and disgust.

Rui, however, took to great lengths to try to protect this "family" even if they all for the most part lived completely terrified of him. Nonetheless the clan's members were all fairly powerful demons who preyed on many humans and spelled the doom of many Demon Slaying Corps' Mizunoto.

Story
After healing their injuries, Tanjiro Kamado, Zenitsu Agatsuma, and Inosuke Hashibira, are sent on a mission in Natugumo Mountain. On their path they stumble into a forest and an injured fellow Mizunoto. Before he tries to warn them of the danger ahead, he is pulled away into the forest by a thread, and subsequently killed.

Tanjiro and Inosuke venture into the forest, only to find it filled with spider webs and with bodies of several Mizunoto lying dead. They find Murata a survivor who explains their members started to erratically attack one another, resulting in a slaughter. The three are soon after surrounded by the moving bodies of their comrades which attack them. The trio defends against them as Tanjiro realized they are being manipulated and there are both corpses and living people mixed. Tanjiro discovers the spider threads are controlling their comrades which are placed by the miniature spider demon around. Inosuke tries in vain to kill them but they are too many, so Tanjiro pleads with him to detect the source of the spiders so they can avoid killing their comrades. Annoyed, Inosuke complies and detects the Mother Spider Demon using his Spatial Awareness. Murata stays behind to fight the controlled Mizunoto while the two went after the Mother.

On the way they fight Ozaki who is also controlled and her attacks made stronger by the manipulation, however the attacks take their toll as she is forced to fight to the point of her bones breaking. Tanjiro has her follow him and then turned on her and launched her into a tree's branch so the threads would become entangled. Inosuke followed suit and did the same with several Mizunoto. The Mother annoyed by this, used her powers to break the necks of her victims, killing them on the spot, which deeply enrages Tanjiro.

Further making their way, the Mother unleashes her strongest puppet monster on the two of them. The monster proves strong and Inosuke sustains injuries in the process, but with a combination attack Tanjiro catapults Inosuke into the air giving him the necessary power to cut the monster, slaying it. Inosuke inspired by this, in turn, launches Tanjiro to the Mother, who realizing her current life full of torment embraces her death with relief as Tanjiro who notices her intentions, gently slices her head so she feels no pain. Before dying the Mother reveals a member of the Twelve Demon Moons is in the clan.

Meanwhile Zenitsu who was left behind ventures into the forest as he realized that Nezuko, his crush was inadvertently thrown into the mountain as Tanjiro carried her so he follows after them to protect her. On his way he stumbles upon a terrifying sight of a house held by spider webs with hanging corpses on the threads. He is then confronted by the Older Brother Spider Demon who tries to prey on him. Zenitsu all too scared to fight tries to keep his distance from him and his spider minions, but is told by the Older Brother that he was bitten by his minion, with the poison already on his body and will suffer several symptoms before ultimately become a minion within 30 minutes, which further horrifies Zenitsu until he falls unconscious.

The Older Brother finds Zenitsu weird but tries to consume him as he fainted, until Zenitsu in his trance starts his rampage, putting the Older Brother on alert. Zenitsu has flashbacks of his training days as he fights the spiders, with the Older Brother realizing Zenitsu is only able to employ a single technique gloating on his alleged victory. Zenitsu remembers his master's saying that if he can master even only one attack, that will be all he needs to achieve victory. Zenitsu pushes himself to his limited and in an instant, defeats the Older Brother. Weakened by the poison he tries to control his breathing to the best of abilities to slow down its effects.

While on the forest, Tanjiro and Zenitsu find the Older Sister Spider Demon who summons the Father Spider Demon while she flees. The Father yields to the Demon Slayers to stay away from his family as he demonstrates his strength, as he almost lands a hit on Inosuke but is stopped by Tanjiro who tries to slice his arm, but it is too hard for his blade. Inosuke tries the same but to no avail, and the two are pushed away by the Father's fortitude. The two try to run away and Tanjiro strategically cuts a tree so it falls over the Father. Tanjiro tries to seize the opportunity to use his strongest technique to kill the Father, but the latter manages to stand up and use the same tree to catapult Tanjiro away from them, Tanjiro yells Inosuke to defend his life until he can help him.

Inosuke is forced to run but the Father discovers his location due to his blood drops. Inosuke tries to run but then disgusted by how he started to think more strategically like Tanjiro decided to fight back against the Father. His first slice sticks into the Father's arm until he uses his second blade to pound the first, slicing the Father's arm. The Father runs away with Inosuke in pursuit and finds him in a tree. Inosuke gloats that the Father is afraid of him, but soon after the demon sheds his skin causing an increase in muscle mass and his arm is regenerated. Inosuke realizes he is outmatched and resigns himself to his fate until he remembers the words of the people he came across, including Tanjiro.

Regaining his senses, Inosuke tries to fight against the Father but is overwhelmed by his speed and power. He finds an opening but his blades break as the Father's body is too hard. The Father grabs him and tries to crush his head as Inosuke has flashbacks of his mother. The Father's arm is then instantly sliced by Giyu Tomioka who timely saved Inosuke from death. The Father regrows his arm and tries to attack Giyu, but the Water Pillar instantly kills the demon chopping him to pieces, leaving Inosuke dumbfounded of Giyu's strength.

After being separated from Inosuke, Tanjiro finds the Older Sister being tortured by Rui. Rui tells Tanjiro to not witness their family matters, however, Tanjiro protests that what he can smell their true feelings and that there is no trust or love between them, just stagnant fear, disgust and mistrust calling their family a fake. A Mizunoto appears and boldly claims he can kill a "demon kid" easily and climb the ranks that way, however, he is instantly mutilated by Rui's web. Rui then turns his attention into Tanjiro angered by his claim that their family is a fake. Tanjiro realizes Rui is a powerful adversary and the two fight, with Tanjiro able to avoid Rui's threads. As Tanjiro is able to smell things again, finds an opening to attack Rui as his blade clashes with Rui's web, cutting his blade in the process.

Trivia

 * The Spider Family where the first group of demons who actively worked together to fight encountered in the series and only other demon group shown, aside from the Twelve Demon Moons of Muzan Kibutsuji.