Delvers

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Delvers (探窟 (たんくつ) 家 (か) , Tankutsu-ka), also known as Cave Raiders, is a general term to refer to adventurers who dive deep into The Abyss to explore its secrets. In the town at the edge of The Abyss, Orth, Delvers are held in high regard as heroes, and many children aspire to become one in the future. They delve into the hellish pit and return with invaluable Artifacts hidden inside, exploring its depths and contributing to the study of the abnormal hole. When deep in The Abyss, Mail Balloons are used to transport light packages to the surface. Orphanages, such as Belchero Orphanage, teach orphans everything about delving, like an academy, granting the the possibility of a bright future to those forsaken by life.

The greatest Delvers are those known as White Whistles, those that have made discoveries and retrieved Artifacts that have changed the world. They are immensely admired by the population and considered to be the pinnacle of Delvers. While many Delvers work individually or in small groups, occasionally, official parties are formed by the government to obtain certain items from The Abyss. Because Artifacts of higher grades can alter the balance of power between countries, illegal Delvers from foreign nations sometimes compete to get their hands on them.

Classification

Delvers are classified with Whistles of different colors based on their ability, experience, and achievements.

Bells

Bells are the novices in training, yet to receive a whistle. This rank is given to those who are studying to become Delvers, but have yet to actually go into The Abyss themselves. Though most bells are given to young children, Reg was also given a bell until his first dive.

Red Whistles

Red Whistles are the apprentices. They are rookie Delvers who have decent knowledge of The Abyss and have descended into the 1^st Layer on their own. It is a common rank for prepubescent kids who have studied from an early age. One obtains a red whistle and the official title of "Delver" after their first descent into The Abyss. While they are fairly knowledgeable, Red Whistles lack the physical fortitude to travel very deep, so they are only allowed to descend to a depth of 550 meters. Going any deeper is treated as an accident or rebellious behavior, a rescue party is sent to retrieve them. If a Red Whistle somehow manages to descend 1,350 meters, to the 2^nd Layer, it is treated as suicide and search parties are called off.

Blue Whistles

Blue Whistles are "proficient". They are more experienced Delvers who have managed to prove themselves. Blue Whistles are allowed to delve into the 2^nd Layer of The Abyss, so they most likely possess an acceptable fighting ability to fend off the beasts of the Forest of Temptation. Typically, and with the appropriate training, one attains the rank of Blue Whistle at the age of 15; though, there are exceptions to this, such as Marulk.

Moon Whistles

Moon Whistles are the assistant instructors. They are highly proficient Delvers that carry an extensive knowledge of The Abyss. Moon Whistles can delve down to the 3^rd or 4^th Layer (sources contradict; see footnote) safely, so their delving ability is in a completely different level to Blue Whistles. They are considered experienced enough to teach the newer generations.

Black Whistles

Black Whistles are the experts. They are extremely talented Delvers that have mastered the techniques of delving. Black Whistles may reach down to the 4^th or 5^thLayer (sources contradict; see footnote) of The Abyss, which is the point at which The Curse of the Abyss can cause one-touch insanity. They also sometimes work under White Whistles as subordinates and assist them in their expeditions.

Unlike previous ranks, in order to become a black whistle one must be recommended by another Black Whistle before attempting a promotion.

White Whistles

"White Whistle (rank)" redirects here. For the physical whistle, see White Whistle (object).

White Whistles are the legends. They are considered to be the greatest Delvers of all. Their achievements have changed the world, and their discoveries astonished all, turning them into spectacular historical figures, called "Nether Stars" (奈落の星 (ネザースター) , "Nether Stars", Star of the Netherworld^?) by some. White Whistles are titled after their unique persona (using "sovereign of" or "lord of") and reach a whole new level incomparable to that of other Delvers. They are armed to the teeth with Artifacts of The Abyss and represent a formidable force. Because of their status, any information that is officially passed by them is considered a fact, no matter how absurd. The same information provided by anyone other than a White Whistle would be declared inconclusive.

White Whistles do not have any depth limit; however, since The Curse of the Abyss make it humanly impossible to survive the ascent from the 6^th Layer, for most of their life, they limit themselves to the 5^th Layer. At some point when they make the decision, a White Whistle will descend into the inviolable 6^th Layer. Since returning from this point is impossible, this descent is called the "Last Dive" (絶界行 (ラストダイブ) , "Last Dive", Crossing of the Absolute Boundary^?), and it represents the most important point of their career: delving into largely unknown territory.

Their whistles themselves cannot be obtained through conventional means. White Whistles are made out of Life-reverberating Stones, which can only be obtained through the remains of a loved one of the Delver. Once the stone is refined into a White Whistle, it will sound only for the Delver for whom it was created, via a hidden insignia. Its sound can bring out the true purpose of some Artifacts.

Delvers

Bells	Red Whistles	Blue Whistles	Moon Whistles	Black Whistles	White Whistles
Kiyui	Nat Reg Riko Shiggy	Marulk	Jiruo Yelme Zapo	Cravagli Gallice Gueira Hablog Neyozel Nishagora Rimeyo Simred Torka Yataramaru	Bondrewd Lyza Ozen Riko Srajo Wakuna

Trivia

• All members of the Umbra Hands are considered Black Whistle Delvers, yet some of them were bounty hunters before becoming Umbra Hands.
• The only White Whistle Delver currently above the 5^th Layer is Ozen.
• Delvers are managed and given their ranks, according to their achievements, by the Delver Guild HQ.
• The colors for the whistle's and ranks were decided by the colors of the night sky. That is why they go from red, blue, moon etc. Red Whistles were made red so it would be easier to pick them out as beginners as the color is not associated with the night sky but more with early morning. The White Whistles are special because they are not part of the night sky theme.
• Red Whistle Delvers are usually 10 to 14 years old and stay in the 1^st Layer. Blue Whistle Delvers usually need to be 15 or older to achieve this rank and are allowed to delve to the 2^nd Layer. Moon Whistle rank is usually reached with about 22 years of age and they are able to live off what they earn by independent excavation while lower ranks, like Blue Whistle Delvers, often have a part-time jobs, such as tourism and service gigs around the town of Orth.
• According to Akihito Tsukushi, certain rules, like the Last Dive, exist for the White Whistle Delvers, but none of them are following these rules.
• A "Sovereign"-title of a White Whistle Delver is determined by their reputation and the person's intentions, and is also registered in a directory. It is said that it started when a member of a White Whistle Delver team began calling them that for fun. Most of the time, the nicknames are the equivalent of something the newspaper or the public started calling them and they became established due to it. These ones aren't registered in a directory.
• White Whistle Delvers are at times accompanied in their last dive by Black Whistle Delvers who are part of their squad.
• People from other countries can become Delvers, but like Riko and the others, they must start with a bell. The key point is following the process put in place by the nation to obtain a whistle after training.
• Red Whistle Delvers have an agreement to generally not get involved with illegal Delvers. They just report the matter and let other people crack down on it.
• Whistles function like a license system. After learning the ways of delving and obtaining a Red Whistle, a practical test is conducted, only after which Delvers finally get their license. It takes time to officially become a Delver, so people who don't want to bother access The Abyss via the slums to try to mine in 3^rd Layer|the Great Fault illegally.
• In the extras of the Collector's Edition Made in Abyss: Binary Star Falling into Darkness, the depth limit for Red Whistles is noted to be 450 meters while in the main series their depth limit for delving being 550 meters. Furthermore, the depth limits in this game are 2,600 meters for Blue Whistles, 12,000 meters for Moon Whistles, and 13,000 meters for Black Whistles.
• According to Riko, whistles used to be made out of cork but, since cork whistles had problems making sounds at stable volumes when wet, they were eventually replaced with their current, improved designs.
• White Whistles are only permitted to own up to First Grade Artifacts, while Bondrewd is in possession of the Special Grade Artifact Zoaholic.