NOTE: This article contains spoilers! Read with caution.
According to various legends in the series, the planet on which the story takes place (presumably Earth) was visited by six meteors, which broke the planet six times, creating six new moons. While it can be assumed that the Lunarians reside on the original moon, this has not been explicitly stated. It is also not known whether anything lives on the other six moons.
The Lunarians are the spirits of humans who have remained trapped in this existence since they cannot pass onto the next world. Prince Aechmea implies that the Moon is where unpurified souls eventually wander to until they can be cleansed with prayer and move on. He states that the Lunarians have been trying to pass on for tens of thousands of years, though presumably souls have resided on the Moon while humans and other animals still existed far before that as well. On the Moon, they have built a small civilization consisting of at least one town-like structure where they reside. This structure contains many facilities such as factories, gardens, laboratories, and places to dine.
For thousands of years, the Lunarians have travelled to the Land to attack and kidnap Gems. At first, they tried to persuade the Gems to cooperate but that did not work so eventually they decided to grind all captured Gems to dust and spread them over the surface of the Moon. They plan to do this for a very long time until the Moon shines with the Gem's shards. They have also kidnapped all of the Admirabilis and use them as cattle. Larger Admirabilis can be seen grazing on the Moon's surface, eating up sand to build their shells.
At some point later in the story, Phosphophyllite infiltrated the Moon by letting themselves be captured. They were able to learn about the Moon and the history of the Lunarians. They made an agreement with Prince Aechmea to bring more Gems back to the Moon in return for the attacks to stop and for the revival of the previously captured Gems.
The Moon consists of mostly barren land dotted with craters. The areas shown in the series seems to be mostly very fine gray sand. Somewhere on the surface is a hill formed by the structure where the Lunarians live. The buildings in this structure has a very geometric stairstep design similar to the pattern of bismuth crystals. It was built out of mineral oils and metals found deep within the Moon. The oil melts every night and hardens again every morning, causing the buildings to change slightly everyday. The structure seems to be about one or two miles or kilometers long. It is unknown if this is the only structure or if there are multiple on the Moon.
The Lunarians hill changes everyday so some locations may not be permanent. Others are implied to have existed for longer periods of time. Note that most of these places are not explicitly named in the series so the names used in this article are for the sake of organization and convenience.
At one end of the hill, the road extends out into a large platform. Here is where the Lunarians disembark and travel to and from the Land. When leaving, the Lunarians adopt the appearance that they are mostly seen with when emerging as sunspots. A large figure stands in the middle with many normal-sized sundries surrounding it. They are then covered in a cloud that is revealed to be both a device for transportation as well as cloaking. The appearance of the sunspots as seen from the Land is in fact this device opening up.
When Aechmea was explaining their people's history to Phosphophyllite, they sat in various locations where they were served food and drinks, including alcoholic beverages. At first, they both ascended a stairway to a dining room with an elegant table set by a large window. After eating here, they moved on to an open area where they sat by a counter. Here, Aechmea indulged in several alcoholic beverages.
The Synthetic Gem Factory
This facility is a large space filled with spheres either suspended or lifted by pillars. Here is where synthetic gems are produced from minerals found on the Moon using heat and pressure. Within the spheres, eight kinds of metals and carbon undergo high temperatures and pressures to create various gems, including diamonds, corundum, and beryl. On the ground floor, the synthetic materials are processed into tools, weapons, or shaped into artificial Gems.
The Synthetic Human Factory
The Lunarians also have a experimental facility meant to create synthetic humans, presumably so that they can pray and purify the spirits and allow them to pass on. It is mostly shown to be a large tank of liquid with moving white strands called "human particles". There is apparently a strange music that plays in this place. Both Phos and Semi did not feel comfortable being here.
- The Lunarians - The Moon is their home until they can find a way to purify themselves and pass on. Among the Lunarians, there are a few notable individuals:
- Aechmea - The leader of the Lunarians, he is adored by them all in the same way all the Gems love Kongo-sensei. They affectionately call him "Prince" as he does not like using his own name.
- Semi - A big and muscular Moon Person who acted as Phos' guide and monitor. They are shown to possess a demon-like battle form when on the Land.
- Barbata - The Moon Person who is in charge of the synthetic Gem factory. They explained to Phos how the factory works.
- The Admirabilis - A species that was kidnapped by the Lunarians for their beautiful shells. They are currently kept as cattle and can be seen wandering all around the surface of the Moon and the hill.
- The Gems - Though technically in suspended animation, all the kidnapped Gems have been ground to dust and spread over the Moon's surface. As part of the deal with Phos, Aechmea says they will try to restore them, but it may take the entirety of their lives.