Riko, a young Red Whistle trainee in Orth, searches the Abyss’s first layer for relics with Nat. When they become separated, Riko finds Nat threatened by a crimson splitjaw and draws the predator toward herself with her whistle. Cornered and unable to escape, she is saved when an unknown blast drives the creature away and melts nearby petrified trees. Tracing the attack, Riko discovers an unconscious boy whose body appears mechanical. She and Nat secretly carry him back to Belchero Orphanage, where Riko hides him from the adults and recruits Shiggy and Kiyui to help revive him. Their improvised electrical treatment causes a blackout but awakens the stranger, who can speak yet remembers neither his name nor his origin. Riko identifies his unusual body, extending arms, and resistance to heat as signs that he is a robot. She names him Reg after a dog she once owned. Escaping the orphanage’s scrutiny, Riko takes Reg outside at sunrise, shows him Orth and the enormous pit below, and proposes that he climbed from the still-unknown bottom of the Abyss.
Episode 2
あらすじ
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Riko and her friends investigate Reg’s body and compare his abilities with known relics. Because nothing similar appears in the official records, Shiggy concludes that Reg may be an Aubade, a supreme treasure whose discovery would lead adults to confiscate and possibly dismantle him. The children therefore invent a background that lets Reg enter Belchero Orphanage as an ordinary amnesiac orphan. Jiruo accepts the story, and Reg begins training as a cave raider. Two months later, Black Whistle Hablog returns from the second layer carrying Lyza’s White Whistle and a sealed document. Orth holds the Resurrection Festival to honor Lyza, while Riko receives the whistle and learns more about her birth. Jiruo explains that Riko was born in the fourth layer, that her father died during the expedition, and that Lyza abandoned a priceless relic to bring her infant daughter to the surface inside the Curse-Repelling Vessel. Riko is then permitted to inspect Lyza’s recovered papers. They contain drawings of unknown creatures, including a figure resembling Reg, and a brief message stating that someone will wait at the bottom of the netherworld.
Episode 3
あらすじ
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Convinced that Lyza’s message is addressed to her, Riko announces that she will descend to the bottom of the Abyss. Nat objects because the deeper layers make return impossible, and their argument ends with both children distressed. During Reg’s first official cave raid, he confirms that ascending does not affect him with the Curse and becomes increasingly determined to learn what he is. He chooses to accompany Riko without being asked, promising to protect her while seeking answers about his own origin. Shiggy supplies a stolen rough map and explains the known layers, their hazards, and the point beyond which messages from ordinary raiders are dismissed as unreliable. Nat harshly suggests that Lyza is already dead, but later regrets it. Before dawn, Riko and Reg prepare to escape the orphanage. Reg says farewell to the sickly Kiyui and misdirects Jiruo, while Nat returns to apologize and guides the group through the wharf district’s hidden entrance. Nat remains opposed to the journey yet accepts that Riko will go. After emotional farewells and promises to send mail balloons, Riko and Reg lower themselves into the Abyss and begin their irreversible expedition.
Episode 4
あらすじ
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Riko and Reg awaken deep in the first layer after descending from Orth through the night. Riko is delighted by the light carried downward through the Abyss’s force field and by how quickly they have passed landmarks that once seemed unreachable. After breakfast, her Star Compass falls into the depths, but Reg produces an envelope secretly placed in his belongings by Jiruo. It contains copied expedition material and a warning that pursuit will begin at dawn, which Riko interprets as a final test of whether they can survive. They leave their camp, evade a silkfang, and race toward the second layer. A lone pursuer catches them with ease, but he is Hablog rather than an orphanage search party. Nat and Shiggy asked him to escort the pair as far as Seeker Camp. Riko refuses because accepting help would undermine the lesson she believes Jiruo intended. Hablog respects the decision, gives them a vaccine and food, and warns them about Ozen the Immovable, the White Whistle who once carried Riko to the surface. Riko and Reg cross into the Forest of Temptation, where no rescue will follow a Red Whistle, and realize that the wilderness itself is now pursuing them.
Episode 5
あらすじ
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In the second layer’s dense Forest of Temptation, Riko uses the direction of amagiri leaves to navigate toward Seeker Camp. A human cry leads Reg toward an apparent victim, but Riko recognizes a corpse-weeper using a dead cave raider’s voice as bait. Another bird seizes Riko and carries her toward its nest. Unable to reach her with his arms, Reg instinctively fires the weapon in his hand, destroying the predator and a broad section of forest. Riko survives the second layer’s ascent strain and names the weapon the Incinerator, while Reg is shaken by how close he came to hitting her. He soon loses consciousness for hours, revealing a serious cost to using it. After waking, he learns that Riko lost her cave-raiding notebook during the attack. They cook the corpse-weeper’s meat, continue into the windy Inverted Forest, and notice a changing symbol on Reg’s helmet. Territorial inbyos force them away from the central route, but they reach the remote Great Porta tree that houses Seeker Camp. When Reg stretches both arms upward to gain entry, an unseen person seizes them and identifies Riko as still alive.
Episode 6
あらすじ
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Ozen lowers the gondola and admits Riko and Reg into Seeker Camp. Riko thanks the towering White Whistle for helping carry her from the Abyss as an infant, but Ozen responds with unsettling remarks about how burdensome the rescue was. She exchanges their whistles for temporary Blue Whistles and assigns her young apprentice Marulk to hear their story. Marulk guides them through the camp inside the Great Porta, shares a meal, and quickly befriends them. Riko examines low-grade relics, while Marulk asks the pair to remain and explore together. Riko declines because uncertainty about Lyza’s condition makes her feel she must continue quickly. During the night, Riko encounters a corpse-like creature wandering the camp and flees in terror. Ozen later reveals that neither Marulk nor Hablog told her what it was. After hearing that Riko is following Lyza’s recovered message, Ozen claims that Lyza is dead, that the whistle and papers were found beside a grave in the fourth layer, and that the short message was not written in Lyza’s hand. Riko still insists on verifying the truth herself. Ozen then leads both children into her private chamber, where the Curse-Repelling Vessel awaits.
Episode 7
あらすじ
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Ozen explains that the Curse-Repelling Vessel does not prevent the Curse as its name suggests. Instead, dead creatures placed inside temporarily begin moving again and instinctively crawl toward the center of the Abyss. She reveals that Riko was stillborn, revived inside the Vessel, and may be driven downward by the same unnatural force. Reg angrily attacks, but Ozen’s strength overwhelms him. She withstands his extending arms, knocks Riko aside, and continues beating him even after he prepares the Incinerator. Reg’s weapon fires through the chamber, yet Ozen survives and displays the relics embedded throughout her body, the Thousand-Men Wedges. After Reg loses consciousness, Marulk summons Ozen’s cave-raider team. Ozen then admits the confrontation was a severe test rather than an attempt to kill them. She believes their present abilities are inadequate for deeper creatures, although she also confesses that Lyza’s supposed grave was empty and encourages Riko to continue. Flashbacks show Ozen training the younger Lyza. Once Reg recovers, Ozen sends Riko and Reg to survive ten days beyond Seeker Camp with their current equipment. She forbids casual use of the Incinerator because firing it leaves Reg unconscious and Riko defenseless.
Episode 8
あらすじ
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Riko and Reg begin Ozen’s ten-day survival exercise in a dark region beyond Seeker Camp. They locate clean water by identifying rohanas, repel a dangerous aquatic creature with fire, and struggle to obtain food while learning to compensate for Riko’s physical limits and Reg’s hesitation. Over several days they refine their teamwork, eventually hunt an ottoba, and preserve enough meat to finish the assignment. Ozen observes from afar and remembers the expedition that brought Riko upward: after Lyza’s husband and newborn child died, Ozen initially considered abandoning the infant and carrying the valuable Unheard Bell instead, but ultimately bore the heavy Vessel to the surface. Riko and Reg return after ten days and pass. Ozen warns them that time becomes increasingly distorted in deeper layers and advises avoiding other White Whistles. Examining the mysterious message, she notes that its material is an unknown, nearly indestructible relic, strengthening the possibility that Lyza lives. Ozen gives Riko the Blaze Reap, Lyza’s damaged weapon, teaches its limited use, and shares closely guarded knowledge about deeper layers. After Marulk’s tearful farewell, Riko and Reg depart for the Great Fault, while Ozen remembers promising Lyza that she would help Riko continue her chosen path.
Episode 9
あらすじ
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Riko and Reg enter the third layer, the Great Fault, a vertical shaft thousands of meters high. Following Ozen’s advice, they descend through tunnels and animal dens rather than exposing themselves on the open wall. A madokajack corners them inside the remains of an ancient ship, forcing Reg to use the Incinerator. The blast kills the predator but attracts the crimson splitjaw that Reg previously wounded. As the creature closes in, Reg succumbs to the weapon’s delayed shutdown and entrusts Riko with protecting him for two hours. Hungry and exhausted, Riko drags his inert body through the tunnels. A fruit-like scent lures her into the stomach of an amakagame, but she cuts her way out and escapes attacking neritantans. Her only route then climbs upward, triggering the third layer’s Curse. Severe nausea, vertigo, and hallucinations tempt her with visions of returning to Orth and reuniting with Lyza, yet she rejects a homecoming without Reg. He finally awakens, drives off the returning splitjaw with the Blaze Reap, and rejoins her. Both acknowledge that neither could have reached this point alone. Emerging from the Great Fault, they see the Goblets of Giants in the fourth layer below.
Episode 10
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Riko and Reg enter the humid fourth layer, where enormous flat creepers form the Goblets of Giants. Reg senses an unseen presence that moves only while they speak, but cannot locate it. Soon an orb piercer attacks. The creature anticipates Reg’s movements, knocks away the Blaze Reap, penetrates their Scaled Umbrella, and drives a poisoned spine through Riko’s left hand. With no safe escape, Reg climbs upward while carrying her. The fourth layer’s Curse causes Riko to bleed heavily and hallucinate, while the poison rapidly swells her arm. Still conscious enough to direct him, Riko tells Reg to break the bone and cut off the limb before the toxin spreads. Terrified and crying, he begins the procedure, but her breathing stops before he can finish. A rabbit-like stranger who has been watching them intervenes, instructing Reg to clear Riko’s airway and perform rescue breathing. Once Riko breathes again, the stranger warns that her condition remains critical and offers treatment at a nearby hideout. Reg reinforces the damaged arm and follows, noticing that the route avoids the Curse. Inside a shelter filled with cave-raiding equipment, their rescuer introduces themself as Nanachi, a Hollow.
Episode 11
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At Nanachi’s hideout, Reg has no alternative but to trust the Hollow with Riko’s life. Nanachi cleans and stabilizes the poisoned arm, explains that the failed amputation damaged it badly, and admits to observing the pair since they entered the fourth layer. Reg meets Mitty, a deformed, nonverbal Hollow who lives with Nanachi. Nanachi says both once belonged to humanity and were changed by ascending from the sixth layer, although Nanachi retained speech and reason. To complete Riko’s treatment, Reg is sent to gather specific resources: demonfish, hammerbeak eggs, glowing grass, and shroombears carrying water-shrooms. He follows detailed instructions through unfamiliar terrain and returns with the materials. Nanachi plants the parasitic mushrooms around Riko’s wound so they can supply nutrients, slow decay, and assist healing. The improvised treatment finally gives Nanachi confidence that Riko will survive. While washing Riko’s stained clothes at a nearby riverbed, Reg finds fields of Eternal Fortune flowers and the lost Blaze Reap. The scene triggers a fragmentary memory of standing near a grave marked by the weapon and hearing a familiar voice. He cannot determine whether the memory concerns Lyza. Back at the hideout, Mitty approaches the unconscious Riko.
Episode 12
あらすじ
選択した言語がないため、Englishで表示しています。
In Orth, Kiyui develops a high fever on his birthday, intensifying rumors of a disease that kills children on the dates they were born. Jiruo takes him beyond the city to a traveling medical caravan, where the symptoms vanish unexpectedly. The pharmacist Mio suspects that the Abyss itself may be involved. In Nanachi’s hideout, Reg panics when he finds Mitty lying over Riko, but Nanachi explains that Mitty has become attached to her and means no harm. Nanachi then demonstrates the structure of the Abyss’s force field with a thin relic. Ascending pushes a person through layered pressure that causes the Curse, while Nanachi can see distortions in that field. This perception also explains how creatures such as the orb piercer anticipate conscious movement. Nanachi trains Reg to act without telegraphing his intentions and guides him during another encounter with the predator. Reg rescues an injured Black Whistle by confusing the orb piercer, restraining its sensory organ, and forcing it to abandon most of its spines. Before the raider leaves, Reg asks him to tell Jiruo that their adventure continues. Back at the hideout, Nanachi makes a difficult request: Reg must use the Incinerator to kill Mitty.