The Abyss is a mysterious, massive vertical hole discovered on an island in the South Beoluska Sea. It is approximately 1,000 meters in diameter and over 20,000 meters deep. It is inhabited by ferocious primeval creatures beyond human control and contains numerous relics of an advanced ancient civilization. The Curse of the Abyss: A terrifying rule where attempting to return to the surface from the depths causes various physical and mental abnormalities, intense pain, or in the worst cases, death. 1st Layer: Light dizziness and nausea. 2nd Layer: Heavy nausea, headache, and numbness in extremities. 3rd Layer: Vertigo, hallucinations, and auditory illusions. 4th Layer: Intense full-body pain and bleeding from every orifice (the layer where Nanachi's partner, Mitty, lost her human form). 5th Layer: Loss of all senses, resulting in clouded consciousness and self-harm. 6th Layer: Loss of humanity or death (becoming a "Hollow" or losing human shape). 7th Layer: Certain death; even if one survives, returning to the surface is impossible. Bell-earrings: Apprentice children. Red Whistle: Novice delvers. Permitted to dive to the 1st Layer. Blue Whistle: Adept delvers. Permitted to dive to the 2nd Layer. Moon Whistle: Instructor-level. Capable of reaching the 3rd Layer. Black Whistle: Expert delvers. Permitted to dive to the 4th Layer. White Whistle: Legendary delvers. The highest rank, permitted the "Last Dive" into the 6th Layer and beyond. Meaning of the Shape: White Whistles are crafted from a Grade II Relic called a "Life-Reverberating Stone (Yourworth)." Because it houses the soul and feelings of a person who sacrificed their life for the owner, its form reflects that person's nature and their feelings toward the owner. The reason every White Whistle has a unique shape is that the "deep affection" or "strong wish" the deceased held for the owner materializes directly into the whistle's form. Known White Whistles ⬇️ Ozen (The Immovable / Ozen the Immovable) Bondrewd (The Lord of Dawn / Bondrewd the Novel) Srajo (The Lord of Mystery / Srajo the Mysterious) Wakuna (The Lord of Guidance / Wakuna the Chosen) Lyza (The Lord of Annihilation / Lyza the Annihilator) Orth: The town surrounding the Abyss, humanity's last unexplored frontier. A giant bowl-shaped city built around the edge of the pit. The center of the town opens into the massive vertical hole serving as the gateway to the Abyss, where many delvers reside. Belchero Orphanage ⬇️ A facility located in the West District where the protagonists Riko, Reg, Nat, and Shiggy live (filled with many young boys and girls). Leader: Jiruo, Moon Whistle, Male. Delving Training: Before becoming Red Whistles, children undergo training to excavate relics in the shallow layers of the Abyss (approx. 50m to 100m deep).