Tanjiro and Inosuke face off against the Father Spider Demon of Mt. Natagumo. Tanjiro unleashes an attack, only to get hurled away by the demon's overwhelming power. Landing near a river, he comes upon the young demon Rui torturing the Sister Spider Demon. When Rui calls their bond of terror and hatred "a family's bond," Tanjiro is enraged. So begins the battle between Rui and Tanjiro.
Giyu and Shinobu arrive at Mount Natagumo and split up to cover more ground.
Tanjiro and Inosuke's blades barely scratch Father. Tanjiro chops down a tree with the Water Breathing, Second Form: Improved, Lateral Water Wheel on the demon, cutting it at its base, but Father uses the tree to block Tanjiro's sword swing and throw him away from the river.
The poison has Zenitsu lose the use of his arms and legs when Shinobu suddenly arrives and lands next to him.
Tanjiro safely lands and follows screams to the Daughter, who is being tortured by Rui. Tanjiro asks what Rui's doing, but Rui states it's between him and his "sister," a family affair, which upsets Tanjiro as that was not what family was. One of the surviving demon slayers arrives, but Rui flings a web he was holding at him and threads cut through the man's bones and flesh, instantly ripping him to pieces. Tanjiro then fights Rui, frantically blocking his threads with his sword, though he has still suffered numerous minor slashes.
Father pursues Inosuke until Inosuke realizes he's acting like Tanjiro and turns and attacks him. Inosuke wedges one sword in Father's arm and pounds it with the other until the sword cuts through the arm. Wounded, the Father flees and Inosuke chases. Father suddenly sheds his skin, becoming larger and more muscular with a new arm, and turns on Inosuke, his speed, strength, and skin density enhanced. Inosuke's swords snap when he attempts to cut Father's neck with his Beast Breathing, Third Fang: Devour and he is punched away. Father picks up Inosuke, about to crush his skull, and Inosuke uses his position to stab his sword with his Beast Breathing, First Fang: Pierce into the Spider Demon Father's neck, though he doesn't flinch.
Giyu rushes over and cuts off Father's arm, making him drop Inosuke. Father regrows a new arm and charges but Giyu quickly kills him with the Water Breathing, Fourth Form: Striking Tide, leaving Inosuke shocked.
Tanjiro becomes able to discern the threads' scent and attempts to cut one to get closer to Rui with the Water Breathing, First Form: Water Surface Slash, only for the thread to cleanly cut through his blade and rush towards his face.
Characters in Order of Appearance