Kirie is a high school student living in the coastal Japanese town of Kurouzu-cho. Rational, compassionate, and deeply devoted to her family and friends, she serves as the grounded focal point as her town slowly descends into hysteria. She is fiercely protective of those she loves and frequently tries to help marginalized people in her community, maintaining a strong moral compass even as the environment around her becomes dangerous and erratic.

Shuichi is Kirie's boyfriend, who attends school in a neighboring town. His daily commute allows him to recognize the strange, spiral-related phenomena infecting Kurouzu-cho long before other residents notice. Grappling with severe anxiety and depression regarding his town's deterioration, he is highly protective of Kirie and constantly tries to warn her of the impending danger.

Mr. Goshima is Kirie's father, a dedicated potter who works out of a ceramics studio near Dragonfly Pond. Following a special commission, he becomes deeply engrossed in creating specific ceramics utilizing local clay. His new work demonstrates a concerning shift in his artistic focus and personal demeanor as he begins spending late nights isolated at his kiln.

Mitsuo is Kirie's younger brother. Innocent and easily influenced, he frequently finds himself caught up in the town's increasingly bizarre events. His vulnerability makes him a constant focus of Kirie's protective instincts as Kurouzu-cho's environment grows hostile.

Ms. Maruyama is a television journalist who becomes stranded in Kurouzu-cho after a severe weather event destroys her vehicle. As an outsider, her shock at the community's physical and moral decay provides a sharp contrast to the desensitized residents, driving a renewed desire among the main characters to attempt an escape.

Mrs. Goshima is Kirie and Mitsuo's mother. She tries to maintain household normalcy and protect her children as her husband's behavior grows increasingly erratic and their town suffers from inexplicable natural disasters. She acts as a stabilizing force for her family amidst the town's collapse.

Shuichi's father is a Kurouzu-cho resident who develops an intense, all-consuming fascination with spiral shapes. He abandons his usual routines to collect anything featuring a spiral pattern, illustrating the early, obsessive grip the town's strange phenomena can exert over a person's mind and body.

Shuichi's mother is deeply disturbed by her husband's strange behavior. Following a family tragedy, her distress over the shape rapidly evolves into a severe, dangerous phobia, severely impacting her mental health and pushing her to take extreme measures to eradicate the shape from her life.

Azami is a beautiful girl from a neighboring town with a distinct crescent-shaped scar on her forehead. She is fiercely confident and enjoys the intense attention she receives from her peers, though she becomes uniquely fixated on Shuichi when he actively resists her charms.

Okada is a male student who falls entirely under Azami Kurotani's spell. Desperate for her affection, he goes to aggressive and manipulative lengths to win her over, demonstrating the toxic heights of adolescent infatuation influenced by the town's atmosphere.

Kazunori is a boy living in the impoverished, centuries-old row houses of Kurouzu-cho. He is deeply in love with a neighboring girl named Yoriko, but their families vehemently oppose the match due to petty grievances, driving the young lovers to contemplate desperate measures to stay together.

Yoriko is a young woman living in the old row houses whose intense love for Kazunori causes a violent rift between their families. She is determined to defy her parents' harsh restrictions and endure physical punishment to be with the boy she loves.

Sekino is a classmate and friend of Kirie who thrives on being the center of attention. Her deep desire for the spotlight and social validation makes her highly susceptible to the town's strange phenomena as she competes fiercely to be noticed by her peers.

Known by the nickname "jack-in-the-box," Mitsuru is a boy who develops an unsettling, aggressive obsession with Kirie. He constantly stalks her and performs extreme, life-threatening stunts to force her to acknowledge his feelings.

Katayama is a sluggish, slow-moving student at Kirie's high school who becomes the target of relentless bullying from his peers. He begins experiencing a strange, localized swelling on his back that rapidly alters his physical capabilities and subjects him to severe isolation.

Tsumura is a cruel student who maliciously bullies Katayama. He justifies his abuse by completely dehumanizing his classmate, reflecting the community's rapidly eroding moral compass as the bizarre phenomena worsen.

Mr. Yokota is a teacher at Kirie's high school. He exhibits a harsh, intolerant attitude toward the unnatural events occurring among his students, actively leading search parties into the woods to violently stamp out the strange anomalies.

Keiko is Kirie's pregnant cousin. Admitted to the local hospital to give birth safely, she soon finds herself caught up in a terrifying and gruesome epidemic specifically affecting the maternity ward's expectant mothers.

Makio is Keiko's newborn baby. Like the other infants in the Kurouzu-cho hospital, he exhibits an unnervingly fast development and displays a strange, demanding connection to his mother that defies natural biology.

Mr. Wakabayashi is a neighbor of the Goshima family in the centuries-old row houses. While he outwardly appears helpful to newcomers, he actively engages in gossip about other distressed tenants and harbors disturbing voyeuristic tendencies.