Delvers

Delvers (探窟家), also known as Cave Raiders, is a general term to refer to adventurers who dive deep into the Abyss to explore it in order to unveil 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 in the hellish pit and return with invaluable Artifacts that were 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. Some orphanages, like the Belchero Orphanage, teach orphans everything about delving like an academy, granting them the possibility of a bright future to those forsaken by life.

The greatest Delvers are the ones known as White Whistles, and they have made discoveries and retrieved Artifacts that have changed the world. They are immensely admired by the population and considered the pinnacle of Delvers. While many Delvers work individually or in small groups, occasionally, official parties are formed by the government in order to obtain certain items from the Abyss. Because Artifacts of higher grades can alter the balance of power between countries, Delvers from different nations, who have to do so illegally, 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, when Reg first arrived at Belchero Orphanage, he was also given a bell until his first dive.

Red Whistles
Red Whistles are the apprentices. They are rookie Delvers who have a decent knowledge of the Abyss and have descended down to the 1st 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 get very deep, so they are only allowed to descend down to 550 meters. Going any deeper is treated as an accident or rebellious behavior, and a rescue party is sent to retrieve them. If a Red Whistle somehow manages to descend 1,350 meters, to the 2nd Layer, it is treated as suicide and search parties are called off.

Blue Whistles
Blue Whistles are the adepts. They are more experienced Delvers who have managed to prove themselves. Blue Whistles are allowed to delve down to the 2nd 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 teachers. They are highly proficient Delvers that carry an extensive knowledge of the Abyss. Moon Whistles can delve down to the 3rd or 4th 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 serve as teachers for 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 4th or 5thLayer (sources contradict; see footnote ) of the Abyss, which is the point at which the strains of ascension 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 by some. White Whistles are titled after their unique persona ("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 strains of ascension make it humanly impossible to survive the ascent from the 6th Layer, for most of their life, they limit themselves to the 5th Layer. At some point when they make the decision, a White Whistle will descend into the inviolable 6th Layer. Since returning from this point is impossible, this descent is called the Last Dive, 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 it was created for and its sound can bring out the true purpose of some Artifacts.

Delvers
Delvers/Bells|Bells Delvers/Red Whistles|Red Whistles Delvers/Blue Whistles|Blue Whistles Delvers/Moon Whistles|Moon Whistles Delvers/Black Whistles|Black Whistles Delvers/White Whistles|White Whistles

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 5th 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 1st Layer. Blue Whistle Delvers usually need to be 15 or older to achieve this rank and are allowed to delve to the 2nd 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 job like tourism 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 entrance in the slums to try to mine in 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.