High school student Yuuichi Katagiri cherishes his close circle of friends, composed of four classmates: Yutori Kokorogi, Shiho Sawaragi, Makoto Shibe, and Tenji Mikasa. However, when the funds for the upcoming school trip are stolen, the incident causes Shiho and Makoto—who had been tasked with collecting the money—to distance themselves from the rest of their class. Soon after, Yuuichi and his friends are deceived into meeting up and knocked unconscious by unknown assailants. After waking, the group find themselves confined in a white room with controversial figure Manabu-kun, who reveals that one of the five has gathered them together to clear their personal debt of twenty million yen. To pay off the amount, they must participate in a variety of psychological games that will test the true nature of their friendship and humanity. Distressed and isolated from the outside world, Yuuichi and his friends need to cooperate to complete the games. But as their concealed feelings and problematic pasts begin to surface, their seemingly unbreakable bond may soon shatter into irreparable pieces.

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.

Many years ago, after the end of a bloody world war, mankind took shelter in six city-states that were peaceful and perfect... at least on the surface. However, Shion—an elite resident of the city-state No. 6—gained a new perspective on the world he lives in, thanks to a chance encounter with a mysterious boy, Nezumi. Nezumi turned out to be just one of many who lived in the desolate wasteland beyond the walls of the supposed utopia. But despite knowing that the other boy was a fugitive, Shion decided to take him in for the night and protect him, which resulted in drastic consequences: because of his actions, Shion and his mother lost their status as elites and were relocated elsewhere, and the darker side of the city began to make itself known. Now, a long time after their life-altering first meeting, Shion and Nezumi are finally brought together once again—the former elite and the boy on the run are about to embark on an adventure that will, in time, reveal the shattering secrets of No. 6.

When he was a young boy, Afro witnessed his father be cut down in a duel at the hands of a man known only as Justice. After taking the life of Afro's father, Justice cast aside his Number Two headband and took the Number One to claim its godly powers as his own. Years later, having obtained the Number Two headband which grants him the right to challenge the Number One, Afro moves forward in his hunt for revenge on the man who murdered his father. There is just one thing that stands in his way—everyone else in the world! Though the Number One can only be challenged by the Number Two, the Number Two can be challenged by anyone. As his enemies gather to try and take the title of Number Two, Afro must fight through a myriad of foes and obstacles if he hopes to reach the Number One and claim vengeance once and for all.