Riko has now obtained a White Whistle which allows her to venture into the sixth layer of the Abyss, known as The Capital of the Unreturned, after surviving the brutal challenges of Idofront. Alongside Reg and Nanachi, Riko embarks on an exploration of this uncharted domain, where the ruins of the promised Golden City can be found. As the trio navigates the unforgiving environment, they come face-to-face with perilous creatures and treacherous terrains. Eventually, they stumble upon a peculiar village inhabited by "hollows," which triggers a creeping sense of disquiet. Despite the unsettling feeling, the three continue onwards to unravel the secrets of the settlement and the lost legacies of the forgotten adventurers who had once taken on the horrors of the unexplored Abyss.