Riko now possesses a White Whistle, allowing her to descend into the Abyss' sixth layer—The Capital of the Unreturned—after surviving the brutal challenges of Idofront. Riko, along with Reg and Nanachi, begins to explore the uncharted domain, which contains the ruins of the promised Golden City. As the trio begins to adapt to their harsh surroundings, they are soon confronted by dangerous creatures and perilous landscapes. Their journey takes them to a village inhabited by strange beings known as "hollows." Despite the creeping sense of unease that greets them, the three continue on their quest to uncover the mysteries of the settlement and the long-lost legacies of the forgotten adventurers who once descended into the horrors of the unexplored Abyss.