Mayu stands at the edge of the Hellish Abyss, surrounded by waiting Veiled Priests. Mio hardens her resolve and moves closer to Mayu, and the ground begins to tremble violently. The Abyss begins to rumble as though roaring. Images from the time of the Repentance fill Mio's head. Erupting Darkness, and Sae appearing from within the Abyss. The next moment, the priests lined up neatly around Mayu fold back and collapse.
"Ahahahaha!" Sae laughs madly.
As the earth's rumbling grows stronger and stronger, Sae changes into Mayu and slowly approaches. She reaches out a hand to Mio's neck...
Mio is confused. The ritual in which the elder sister kills the younger. Does Mayu have to kill Mio, or does Mio have to kill Mayu...?
"You won't escape again..."
"Mio... My leg hurts... It aches..."
"I won't let you go..."
"Whatever happens, I'll forgive you."
"Are you leaving me again?"
The mind of Sae, who once fell into the Abyss and was then resurrected by the Darkness, is in turmoil. Sae becomes Mayu, and Mayu transforms into Sae.
Mayu's heart. Sae's heart.
Their pure feelings mix with the darkness in their souls, and they suffer as they change into one another. Mio doesn't know what to do.
A tremor occurs that is more powerful than any the Hellish Abyss has so far caused, and Mio loses her balance. Darkness erupts from the Abyss, spreading like a plume, swallowing Mayu from behind.
As soon as Mio, who had been hesitating, sees Mayu enveloped by the encroaching Darkness she forgets fear or bewilderment, and rushes over to Mayu as though flying into the midst of the Darkness...
Mio dives into the Darkness. She proceeds, seemingly pushing it back, though she can't go far as though everything is in slow motion. Her figure becomes overlapped with the image of Mio in a yukata, when she and Mayu became separated at Kureha Shrine's Shadow Festival, pushing her way through the people who seemed like a black wave.
Mayu calls out, crying, above the hustle and bustle of the festival. Mio pushes back the black wave as though pulling at the space between her and Mayu, desperately going on with gritted teeth. Finally she pushes through the darkness and reaches Mayu.
When Mayu notices Mio, her shocked face lights up and she lunges at Mio. She buries her face in Mio's chest as she cries.
"Mio! Mio! I'm sorry!"
"We'll be together forever. We promised."
Mio holds Mayu tightly as she, too, cries.
The scene of the festival disappears. Mio and Mayu, standing embracing at the edge of the Hellish Abyss, change into Yae and Sae. Their facial expressions are ones of satisfaction. They look at each other. Yae's face alone looks slightly sly, and she reaches both hands out to Sae's neck. When Sae notices she smiles calmly and holds out her neck as Yae wraps her hands around it. It is their strangling game, their secret "becoming one" game they have played since childhood.
Yae and Sae, Mio and Mayu put in their strength. The two gradually melt into the crushing darkness. The space between them slowly lessens... Everything is enveloped in Darkness, silent.
In the pitch blackness, Mio and Mayu sit side by side, wrapped in a kimono. Mayu's head rests on Mio's shoulder. Mio embraces Mayu. Their hands are still tightly wrapped.
"Mio?" Mayu says in a whisper.
Mayu's face is calm. "...It's nothing."
Mio and Mayu vanish as though melting together, and the kimono flutters to the ground. From inside it, two crimson butterflies clumsily begin to flutter.
The mountain stream of Mio and Mayu's memories. Sunlight floods through the trees in the forest, where two crimson butterflies fly around playfully.