When the soul-blood curse runes in the Arctic Ice Abyss awaken an ancient pact, and tribulation flames on Spiritcloud Peak burn away a thousand years of obsession, a battle of cause and effect spanning time and space begins.
Su Yu, peerless in both medicine and Gu arts, enters the world carrying half a jade slip of prophecy, only to reunite in the Arctic Ice Abyss with Lin Wantang, a sword spirit successor who possesses fire Gu. The Gu markings on the two of them perfectly match the symbiotic marks of the first Gu Immortal and sword spirit depicted in a forbidden-land mural. As the shadows of twin butterflies appear in the ice, time and space within the mirror collapse, forcing them into the fated vortex of "the bearer of the cauldron using their own body as bait to resolve the cause and effect of every cycle of reincarnation." The sword spirit's ice coffin from a past life, the sect leader's golden Gu egg in this life, and the fragments of time and space inside the nineteen mountain-guarding cauldrons all point to a shocking secret: the Chaos Gu Core is not the source of calamity, but a symbiotic vessel for the obsessions of all who have reincarnated.
As world-devouring Gu insects gnaw at the threads of cause and effect, and Gu chains spanning time and space lock twin souls in a closed loop, Su Yu and Lin Wantang realize amid the interweaving auroras and tribulation flames that the true way to break the Gu curse is to let light and shadow coexist in the heart like butterflies. Using blood to redraw the threads of cause and effect and their hearts as mirrors to shatter illusion, they cleave a path to survival through nineteen layers of reincarnation's lingering shadows, making prophecy a beginning rather than a shackle.
The twin butterflies beat their wings, heralding both destruction and the dawn of rebirth. As glazed pavilions rise atop Spiritcloud Peak and two-colored lotuses bloom in the snow, this "journey of self-discovery" spanning a thousand years will finally reveal the Gu domain's most astonishing truth: the darkness you fight is simply the other pair of wings belonging to your own soul.
