Miku's older brother, Mafuyu, arrives at a large Japanese mansion in the mountains. His friend and benefactor, the novelist Junsei Takamine, and others came to Himuro Mansion to investigate and went missing. He goes inside and exits into a hallway, where he sees Takamine go by. When he finds a dropped schedule notebook on the second floor of the living room, images flow through Mafuyu's head. An ominous shadow following the three as they walk through the mansion's hallways... Mafuyu is now confident that Takamine's group came here. As Mafuyu worries about the safety of Takamine, an ominous shadow creeps up on him. He senses its presence and raises the camera. The camera that has the power to seal ghosts by storing them in photographs.
He somehow seals the ghost and returns to the hallway, when something attacks from inside the mirror behind him... And then...
Arriving at Himuro Mansion to search for her brother, Miku sees the Camera Obscura he should have carried with him. When she touches it, a sinister vision flashes through her head. Then, Miku sees Takamine's party, who had gone missing. They were killed by the Rope Curse of a woman in burial costume named Kirie. The novelist's assistant, Hirasaka, had her limbs torn off by Kirie. Takamine had determined that the only way to be rid of the curse was to return the Holy Mirror, broken into five pieces, to its previous state, and set about doing so with all of his might.
Miku obtains a piece of the mirror in Narukami Shrine, where Takamine died. As she does so another horrible vision flashes through her mind. Turning around, she sees Kirie slowly emerging from the large mirror in the shrine. "You will feel the same pain as me..." Kirie says as she grabs Miku's arm, and her vision goes black...
"The Demon... you're the new Demon..." says a faint voice as Miku awakens in the Doll Room. When Kirie grabbed Miku, she took her back to the past, bringing her closer to the occurrence of the heart of the incident. At the same time, the curse intensifies, and five rope marks appear on her hands, feet and neck. Now Miku notices that she is surrounded by children. These are the ghosts of the children who were Spirited Away in the middle of playing Demon Tag. One of them holds the mirror piece Miku had in his hand. "Give it back..." she says, as the children suddenly vanish.
She suddenly notices a note left by Mafuyu at her feet. Because of the twist in time within the mansion, Mafuyu can't meet with Miku, but he appears to be chasing the origin of the mansion's curse. She sees an imprinted image of her brother disappearing into the Banned Path through the Demon Mouth. Then, Miku is attacked by the ghost of the Blind Demon wandering around the mansion. To create the "Demon" necessary for the ritual to determine the Rope Shrine Maiden, the woman would be blinded by a mask she wore, and even now wanders the mansion. Miku chases after the children, and the Blind Demon's ghost chases after Miku. Two simultaneous games of Demon Tag unfold.
The children who were Spirited Away whilst playing Demon Tag were Mikoto, the daughter of Ryozo Munakata, a folklorist investigation Himuro Mansion's rituals, and her friends. In order to investigate the Himuro family's rituals, Munakata, his wife Yae and their daughter Mikoto moved to the mansion. He figured out that he needed the Blinding Mask to open the Banned Path, the way into the Rope Altar where the ritual was performed. That was the same door Mafuyu disappeared through.
When Miku obtains the Blinding Mask and opens the door to the Demon Mouth, she is attacked by Munakata's ghost, during which she is pulled into a vision. Once, Munakata opened this door and died. Is something inside there...? In the Banned Path is Munakata's warped corpse. Miku reaches out to take the piece of the Holy Mirror clutched in his hand, and Kirie appears again.
A fragmented image of the ritual... a man in a demon mask slaying a priest... While having such a vision, Miku wakes up before the door to the Demon Mouth. Rope marks appear on both of her ankles, and next the marks will appear on her neck and the curse will be complete. The presence of ghosts within the mansion is growing. She sees her brother go into the collapsed Banned Path. Miku learns from Munakata's research books that another path descending to the Rope Altar exists in the Moon Shrine, and heads there.
The destruction of Himuro Mansion was entirely caused by a disaster called "The Calamity", which arose from the failure of the Strangling Ritual. It is said to have occurred due to Kirie, the Rope Shrine Maiden who was raised in order to be killed, being too attached to this world.
From the Moon Shrine Miku descends into the Moon Well, entering the underground. There, she sees an armless and legless female Sokushinbutsu mummy enshrined in a small shrine. Exactly what kind of ritual was the Strangling Ritual? Miku discovers a piece of the Holy Mirror beside the mummy.
Miku picks it up and Kirie appears at the bottom of the well. Just as she is almost about to be captured by Kirie and the curse completed, she hears a voice whisper, "Over here!" from above. Looking up, she sees a girl in a white kimono reaching out her hand. The second Miku grabs her hand, her vision goes black.
Miku wakes up in the Koto Room. It is the day the Strangling Ritual is to be performed. All around Himuro Mansion it is eerily silent. A girl leads her to discover a hidden passage, at the end of which is a strictly guarded confinement room. When Kirie was 7 years old she was chosen as the Rope Shrine Maiden, and as such was raised here, all the while tied up with ropes. Here, Miku sees the girl who has been leading her so far tied to the Torii gate in the room. Miku realises that the girl is Kirie as a young girl. Kirie's heart, in which she wants to stop her own rampage, has turned into her girlhood form, and is showing Miku the way. To run away from Kirie, who again appears from out of the mirror, Miku descends into the Moon Well. There, she witnesses the events of the day of the Strangling Ritual. A ritual in which both arms, legs and the neck were tied to a contraption using ropes, and finally all of the limbs torn off...
On the other side of the Rope Altar, the Hell Gate towers majestically. It is said that when the Hell Gate opens completely, this world and the world of Hell will be joined together, and all of the dead will return. In order to seal this gate, the Himuro family sacrificed a Shrine Maiden, repeating the Strangling Ritual over and over.
When Miku arrives there, she sees Miku absorb Mafuyu. To save her brother she tries to seal Kirie away, but the Camera Obscura breaks. Before Miku, who is seized by despair, appears Little Kirie, who points to the broken Camera Obscura. Inside the camera is the final piece of the Holy Mirror. Placing the completed Holy Mirror on the stone monument in front of the gate, a a dazzling light engulfs Kirie and returns her to her true, conscious self. The recovered Kirie faces the gate. She offers to use her own body to stop the Calamity. Kirie endures the gates trying to open. The cave begins to collapse from the impact. Miku moves to escape. However, Mafuyu resolves to remain there alone. He feels compassion for Kirie, who must seal the gate forever.
Miku awakens alone in front of Himuro Mansion. She no longer sees "impossible things".