After surviving the brutal challenges of Idofront, Riko now possesses a White Whistle, allowing her to descend into the Abyss's sixth layer—The Capital of the Unreturned. Alongside Reg and Nanachi, Riko begins to explore the uncharted domain, where the ruins of the promised Golden City are located. As the trio starts to adapt to the harsh environment, they soon encounter dangerous creatures and treacherous landscapes. Their expedition leads them to a village inhabited by strange beings known as "hollows." Despite the creeping sense of unease that welcomes them, the three venture onward to uncover the mysteries of the settlement and long-lost legacies of the forgotten adventurers who once descended into the horrors of the unexplored Abyss.

Recap of the first 12 episodes of from Noi's point-of-view.

Meg, faithful and gentle, Jo, independent and energetic, Beth, quiet and shy, Amy, amiable and precocious–the four sisters live vigorously and happily at home with their gentle mother while waiting for their father to return from the Civil War. Helping each other, they challenge their fates and grow up to become wonderful women.

Luo Xiaohei is a young monster who normally takes the form of a small black cat. Living freely in the forests, gradual deforestation and human development force him to flee and find a new home. Wandering the city streets, the black cat struggles to survive until he encounters Feng Xi, a fellow monster who takes Xiaohei to an isolated island inhabited by a small group of monsters. Excited to find what he thinks is his new home, Xiaohei lives with the monsters for only a short time before Wuxian, a human Guild Executor, arrives on the island in pursuit of Feng Xi. Feng Xi and his companions manage to teleport off the island, leaving Xiaohei and Wuxian alone. Though Xiaohei refuses to cooperate with the man who attacked his friends, Wuxian forces the black cat to travel to the Guild along with him. Embarking on an uncertain journey, Xiaohei is exposed to a new perspective on the relations between humans and monsters in a rapidly changing world.