Tanjiro and Inosuke are battling Corps members that have been captured in the webs. The two head deeper into the mountain, as they slash the threads while destroying the webs.
The further they go, the thicker the threads become. And those that are being controlled move in ways impossible for a human being.
Trying to stop their moves without hurting them proves to be even more difficult than before, but then Tanjiro makes a certain move…
After scanning the landscape of the forest with his Beast Breathing, Seventh Fang: Spatial Awareness, Inosuke locates a demon in the distance. After informing Tanjiro, he commends his partner for his skills but they continue to get attacked by the controlled Demon Slayers. Elsewhere, Zenitsu has entered the forest in search of Nezuko, exhausted from running hard into the woods.
Inosuke prepares to kill them all, but Tanjiro denies his plan and tries to find another way to stop them. When one attempts to slash at him, Murata blocks the blow, instructing them to leave him and carry on. Despite his lesser skill and cowardice earlier, Murata declares he is still a Demon Slayer and will find a way to fend them off, armed with the knowledge of the threads and avoiding the spiders. Appreciative, Tanjiro grabs Inosuke and they run off to leave Murata, though Inosuke is annoyed at not being able to punch Murata first, for insulting him.
As they travel further into Mount Natagumo, Tanjiro scolds Inosuke for his behaviour; Inosuke justifies himself by claiming Murata insulted him first, calling him "Monjiro", to his chagrin. Tanjiro asks if they are heading in the right direction; as he claims his senses are never wrong, Inosuke runs into several spider webs to his annoyance. They then encounter more controlled Demon Slayers, including a girl who has killed her entire troop. She begs them to not get closer and to summon a higher ranked member.
As she continues controlling the Demon Slayers, the female demon finds joy in anyone getting closer to her, as her nearer threads and dolls are stronger. Suddenly, a voice calling her "Mother" resounds from behind, startling her. The short pale demon from earlier asks if she is able to kill them. Terrified, Mother initially doesn't answer the demon, Rui. Rui claims she is taking time and asks she hasten her efforts or he would tell "Father". Frightened at what might happen, Mother claims she can win and that she will protect him, begging Rui not to tell Father. Rui only tells her to hurry up, before leaving.
Now with the threat of punishment present, Mother forces her dolls to fight harder, unwilling to suffer the consequences. The controlled girl yells for Tanjiro to run but she suddenly swings her blade at incredible speed. She states she is being controlled and was never this strong normally; the threads on her body suddenly contort her arms back, breaking them at the joints. As she screams in pain, she continues to attack Tanjiro. Seeing the demon is ignoring her pain, Tanjiro calls this cruel. Mother then decides to use the rest of the dolls and several more Demon Slayers appear to face Tanjiro and Inosuke. One of them begs for death, as his arms and legs are broken and his bones are piercing his organs, leaving him in agony.
As Tanjiro regards this scene in horror, Inosuke runs in and offers to kill him. Tanjiro, still wanting to help him, signals for him not to. Annoyed, Inosuke calls him out for repeatedly denying his attacks, stating he is blatantly wanting to die. He is forced back as the controlled Demon Slayers corner him with Tanjiro. Knowing the threads will only be attached again when cut, Tanjiro thinks of a new plan. He lures the controlled girl by running away, forcing her to chase him. He spins back around and grabs her in his arms. Using his Total Concentration Breathing, Tanjiro uses his enhanced strength to fling her into the high branches, entangling the threads and preventing them from controlling her.
Seeing this, Inosuke becomes excited and wants to copy his moves; he lures the other Demon Slayers into running after him and throws him into the branches. Unable to control the tangled threads, Mother deems the controlled Demon Slayers useless and decides to use a different doll. Now too scared to continue walking, Zenitsu feebly calls out to his friends and his sparrow Chuntaro. He apologizes for his burdens and suddenly hears Chuntaro atop his head. Chuntaro turns his head to ignore him but Zenitsu excitedly grabs his friend and thanks him for coming back; he calls the little bird cute but only second to Nezuko and sets out to find her again.
With just one Demon Slayer left to restrain, Inosuke and Tanjiro close in on him to tangle threads in the trees; Inosuke had been making their objective a game to beat Tanjiro, seeing who can disable more dolls. Mother curses her humans dolls as useless and manipulates the threads attached to their heads, snapping their necks to Tanjiro’s horror. Inosuke curses the fact they all died despite their efforts but Tanjiro only approaches the closest Demon Slayer’s body. As he kneels down to be near it, he releases his rage and anger without saying anything, startling Inosuke into silence. Tanjiro gets up and states they must go on, to which Inosuke quietly agrees.
They continue travelling through the forest; Inosuke leads them in the right direction and Tanjiro finds that his sense of smell is returning. He detects two demon scents and senses something in the distance. Having detected it already, Inosuke charges forward to decapitate the threat. But as he leaps into the air and lands to attack, he finds it does not have a head and narrowly misses getting cut. They see it is a giant headless demon doll, controlled by the threads and weaponized with blades as its arms.
Zenitsu makes his way slowly in the forest, calling out to Nezuko and Tanjiro. He becomes frightened hearing something in the distance but sees it is simply a flock of birds. Now becoming frustrated, he promises to find Nezuko and leave the forest; he continues calling her name out loud and doesn’t notice he is being followed.
Tanjiro and Inosuke dodge getting hit by the doll, while the latter notes it doesn’t have the usual weak spot, a head. As he wonders how they will attack, Tanjiro states they will slice its body diagonally from its head to its waist with a monk’s hood cut. Inosuke impatiently attacks and lunges forward without waiting for Tanjiro. The doll hits him, cutting Inosuke with minor slashes to his body. Deeming the doll fast but still manageable to attack, he fails to notice the spiders on him and is restrained in numerous threads. Inosuke is nearly cut in half but is saved when Tanjiro parries the blow to the side. Cut free from the threads, Inosuke becomes giddy at the sight of someone getting the better of him.
Tanjiro tells him they must work and think together. As the doll prepares to attack them again, Tanjiro crouches down and signals for Inosuke to launch himself off of Nezuko’s box. He climbs atop the box and slashes both of the doll’s arms. Tanjiro then signals for him to get higher; Inosuke leaps upwards while Tanjiro uses Water Breathing, Fourth Form: Striking Tide, slicing the doll’s legs off. He gives the signal for the monk’s hood cut while Inosuke notes that the whole plan is flowing like water, as naturally as Tanjiro is intending.
As he descends, he realizes Tanjiro doesn’t look at the first attack but the entire battle, commending him. Inosuke lands down and uses both his blades to slice the doll’s body in half, killing it, to Mother’s shock. Tanjiro congratulates him for the finishing blow but Inosuke stays still, ignoring his praises. Instead, he sprints towards him and declares that he can do anything Tanjiro can do; grabbing him, he hurls Tanjiro high into the air. As he is launched, he detects the scent of a demon, realizing it is what Inosuke had detected.
As Mother becomes scared that even her most powerful doll was killed, she shifts the blame to Rui’s earlier threats and why she panicked. She then looks up and sees Tanjiro descending towards her; he breathes in and positions his blade to use First Form, Water Surface Slash to kill her. She becomes terrified at her impending death but suddenly calms herself, muttering that with death, she can be released and know peace. Seeing that she has fully surrendered, Tanjiro changes his form and uses Fifth Form: Blessed Rain after the Drought, bringing her a peaceful death. Mother notices she feels as if she is showered by a gentle rain, not in any pain at all but instead feeling warm.
Never imagining her death could be so peaceful, she states she can be released. Mother remembers a moment in the past, when she was harshly wounded by an immense, spider-like demon, Father. She apologizes to him and asks why he is mad. Rui only taunts her for not knowing what had displeased him. Another demon appears from behind, laughing that “Mom’s in trouble with Dad again”. Mother is then grabbed by the hair by Father and hoisted up, causing her immense pain, as another pale female demon watches the scene.
Mother looks at Tanjiro’s eyes and comments on their kind appearance; she remembers that while she was human, someone had looked at her with the same expression. But as she tries to remember her past, she fails to recall the details, instead stating it must have been someone who treasured her. She then wonders what that person is doing now, with tears in her eyes.
In her final moments, Mother thanks Tanjiro by informing him that a member of the Twelve Kizuki is on the mountain, wishing him to be careful as she fades completely. Tanjiro, hearing her final words, becomes stunned that a genuine member is on the mountain.