The movie opens with a young high school girl named Kirie Goshima, telling us about some strange events that took place in her hometown. Looks like the movie wasted no time in getting to the horrific part; a high school boy dies falling from a spiral staircase. A few days before the gruesome incident; Kirie Goshima, the young high school girl is staring at the town where she lives, right when a gust of wind hits her out of nowhere, giving her an uneasy feeling.
On her way back home from school, Kirie encounters her weird classmate, Yamaguchi, who suddenly appears on her way to surprise her, and propose her to be his girlfriend. But, by treating Yamaguchi lightly, Kirie manages to avoid him, and make her way home. However, in the middle way, she notices something strange about her boyfriend Shuichi's father filming snail shell in a rather eerie manner.
Kirie attempts to greet him, but he continues recording without acknowledging her presence. Ignoring the situation, the girl heads towards the tunnel to wait for Shuichi, who soon arrives on his bicycle to give her a ride home. They then make a stop at a nearby park along the way, where Kirie tells Shuichi that she sees his father recording a snail shell.
Shuichi, visibly distressed, tells her that his father has been acting weird lately. He implores Kirie to elope with him, but she politely declines his plea. Upon reaching her home, Kirie notices her father, Goshima, engrossed in crafting a spiral-patterned pot.
To her surprise, Shuichi's father is also there, passionately filming the spirals on the pot. He expresses his desire for Goshima to create a spiral plate for him, exhibiting his peculiar fixation with spiral patterns. Even though Goshima agrees to fulfil his request, Shuichi's father keeps acting strangely in front of them.
The next day at school, as Kirie and her friend, Ishikawa, make their way to class, they are intercepted by the weird classmate again. Yamaguchi confesses his feelings for Kirie, and proposes that she leave Shuichi for him. However, due to her strong bond with Shuichi since childhood, Kirie rejects his advances.
As they walk along the hallway, the two friends don't notice that the other students are standing in a creepy way. And then all of a sudden, A fellow classmate tragically ends his life by leaping from the spiral stairs. Kirie rushes to the restroom to compose herself, and inside, she unexpectedly comes face to face with Sekino, the popular girl from their school, accompanied by her two devoted followers.
Sekino boldly asserts that it was merely a desperate cry for attention, and believes the boy took his own life in order to gain the spotlight, as attention is something that many students, including herself, yearn for. When Kirie discusses her classmate's death with Shuichi and questions the circumstances, he cryptically mentions a spiral obsession. Shuichi reveals that the boy died due to helix, and discloses that their town is cursed by Uzumaki, causing people to exhibit abnormal behaviors around anything spiral-related.
As they continue their conversation, it turns out that Yamaguchi is lurking behind the tree. Trembling with a mix of anger and despair, he can't stand seeing Kirie with Shuichi. Shuichi continues his confession to Kirie that his own father has stopped going to work; he’s now collecting various spiral items, and isolating himself in a room filled with them.
However, the most shocking revelation is what his father did the previous night, when Shuichi’s mom cooked a dish with an Uzumaki pattern. When Kirie expresses doubt upon hearing Shuichi's account, he invites her to his house to witness his father's state firsthand. As they arrive at Shuichi's home, they are greeted by his mother's screams.
It turns out that Shuichi's father is enraged at his mother for throwing out his collection of spirals, which, unbeknownst to him, Shuichi was the one who did it. Despite their efforts to convince him to return to normal, his father remains obstinate, declaring that they cannot rid him of his love for spirals, as he can now manifest spirals within his own body. Kirie loses consciousness upon witnessing this disturbing sight.
On a rainy day, Kirie musters her courage and heads to school, where a series of strange events begin to unfold. All of a sudden, a student named Katayama, known for appearing only on rainy days and covered in slime, arrives late to class. One of his classmates, Tsumura makes fun of him by saying that even a snail moves faster than he does.
As Katayama stumbles, his slime falls onto Tsumura's face, provoking Tsumura's anger, and something strange that looks like a snail's spiral shell is starting to grow on Katayama's back. After the school concludes, Kirie finds herself once again confronted by Yamaguchi's sudden presence. This time, he surprises her with a gift box, which she cautiously opens.
A horrifying joker face springs out; Kirie pushes Yamaguchi to the ground, and she calmly informs him that he is simply not her type. At home, her father requests that she carry the spiral plates made for Shuichi's father. Even though it scared her to see how Shuichi's father used to act, she arrives at his house, but finds no one at the door.
Despite the absence of any response, Kirie hears a loud noise coming from inside the house, and decides to investigate. When Shuichi and his mother come home from the doctor, they hear Kirie's scream, and discover Kirie on the floor in a horrifying state, pointing towards the washing machine. They are shocked to find Shuichi's father's lifeless body inside, but we are uncertain of the body's condition.
During his father's funeral, Shuichi confides in Kirie that he had foreseen his father's death in a similar manner, but then suddenly. . .
Shuichi’s mother cryptically informs him that his father is in the sky, making him look up and witness a descending whirlpool of smoke. He promptly takes his unconscious mother to the hospital in an ambulance with Kirie accompanying him. However, en route, Kirie notices the whirlpool heading towards Drgonfly Pond, leaving her stunned.
After admitting his mother to the hospital, Shuichi once again urges Kirie to elope with him before it's too late, but they must remain in town for a few more days due to Shuichi's mother's treatment. They then encounter Ichiro, a reporter who reveals that Shuichi's father had visited him days before his death. He delved into the town's history and persistently asked about Uzumaki, the spiral.
Ichiro's revelation piques their interest, and they decide to help him in his investigation. Shuichi shares all his father's recordings, from filming snail shells to his untimely demise, with Ichiro, who notices that Shuichi's father placed his wife's mirror inside the washing machine before stepping into it. But the exact reason behind his demise remains elusive even after reviewing the recordings.
Nevertheless, Ichiro remains determined to scrutinize the footage. After the investigation, Ichiro offers Kirie a ride home. They are both astonished to see a scary figure, who turns out to be Goshima, covered in mud.
He casually tells them that he returned from Drgonfly Pond, where he went to gather mud for his pottery, leaving them bewildered. Meanwhile, Shuichi remains at the hospital to care for his mother; but when he checks on her, his hands are inexplicably drenched in blood. He then discovers that she has been consumed by the spiral, and that she cut her fingertips upon noticing the spiral patterns on them.
Back to Kirie; she decides to go back to Shuichi's home. It turns out to be a nightmare; a haunting dream in which she dies inside the washing machine, much like Shuichi's father. Awakening abruptly, she tries to calm herself, but then she hears a glass break.
When she goes to investigate the noise, she remains dismayed to find Goshima feverishly working on a pot late at night. As the father realizes Kirie has seen him, he becomes angry, and after she leaves, Goshima continues his work, gazing into the fire with spiral formations in his eyes. As time passes, the curse spreads throughout the town, ensnaring students in its grip.
Kirie observes Sekino with her hair spiralling absurdly in the gymnastics class. Meanwhile, Tsumura who has previously had a slime splashed in his face, begins drinking excessive amounts of water, and develops a snail shell on his back. Back to Ichiro; he spends the entire day tirelessly researching the cause of Shuichi's father's death, and the role of the mirror in the washing machine.
He keeps trying to learn more about the history of the curse, and finds that the curse has something to do with a mirror retrieved from Drgonfly Pond, which belongs to an old cult. When Kirie brings spiral-frosted cakes to Shuichi's mother in the hospital, Suichi decides to discard them all, as his mother now suffers from a spiral phobia. The two then walk up to Shuichi’s mother’s room, covering the spirals on their bodies with gloves and a beanie.
Not only did his mother get rid of fingerprints, but she also got rid of a spiral in her hair. Shuichi then receives an urgent phone call from Ichiro, requesting his immediate visit to Drgonfly Pond. Ichiro claims to have crucial information regarding his father's death, and the truth behind the spiral curse.
In a hurry, Shuichi leaves the hospital, tearing an ear pamphlet to shreds upon noticing a spiral shape inside. He fears that his mother may harm herself if she discovers a spiral formation in her ear by chance. On their way to Drgonfly Pond, Shuichi and Kirie encounter Yamaguchi, who seems desperate for Kirie's attention.
Frustrated by Kirie's choice of Shuichi over him, Yamaguchi rushes towards the road, intending to do something reckless. As a result of the tragic accident, Yamaguchi and Ichiro die horribly. After the unsettling incident, Shuichi and Kirie continue their visits to Drgonfly Pond, but now they don't know what Ichiro might have to say about the spiral curse.
Here Shuichi reassures Kirie of his unwavering commitment to protecting her. Later that night, inside the hospital, a bug slowly makes its way toward Shuichi's mother's bed. She hastily tosses the bug onto the floor, quickly killing it with a plant pot.
Not satisfied with the mere attempt, she decides to eliminate the bug entirely. But as she descends from the bed, clutching a piece of paper, she notices a strange sight before her eyes—a swirling spiral. Within the spiral, she sees her husband's face, his tongue contorted into a twisted coil, asking her why she hates spirals so much, when she has one in her own ear.
In a moment of anguish, she picks up a shard of the shattered plant pot, and forcefully strikes her ear, tragically bringing an end to her own life. On the next day, whirl-like clouds appear in the sky, and during Shuichi's mother's funerals, they are accompanied by smoky, ghost-like faces of victims who perished in spiral-related ways. Elsewhere, it is revealed that Kirie's school teacher, has fallen victim to the spiraling curse, as evidenced by the spiral pattern adorning his back.
The strange occurrences in the town gain notoriety, spreading throughout the city. News crews arrive, capturing the unsettling events through their camera lenses. The dominance of the spiral curse becomes even more apparent as giant human snails crawl on the school walls.
The news broadcasts the strange behaviour of students, including Sekino, whose hair has grown into long, extended spirals, and her followers in the name of spiral victims. Upon witnessing these incidents on television, Shuichi and Kirie make a swift decision to leave the town immediately, intending to bring Kirie's father along. However, they discover that he is nowhere to be found.
Kirie then finds pots adorned with spiral patterns, and her father's discarded lucky charm, which he had always kept close. And then all of a sudden, Here Shuichi’s lower body is also twisted by the Uzumaki curse, and he urges Kirie to save herself and leave the town, but Kirie refuses to abandon her childhood friend. Unfortunately, Shuichi's body completely contorts into a spiral pattern now, resulting in his untimely death.
But then… Kirie soon encounters Shuichi's transformed, spiralled figure, which attempts to draw her into the curse, coaxing her to join the spiralling fate. With this incident, it becomes clear that the spiral curse has engulfed the entire town, leading every individual to succumb to its influence and meet their demise. Finally, the spiral smoke created in the sky leads back to the Drgonfly Pond, the source from which the spiral curse originated.
