Cheongsu

Cheongsu (청수) is an inhabitable planet in the Jeobseon Cooperative. The second planet in the Cheongsu System, it orbits its star Sejong-14 with five other uninhabitable planets. It is home to a population of 9.2 billion. A water planet, the surface of Cheongsu is primarily covered in ocean with a few scattered islands, as well as ice packs at the poles. Underwater landscape mapping reveals that the planet has just recently emerged from a cataclysmic global ice age less than 2 million years ago, the cause of which is currently being studied.

Due to the aquatic terrain of Cheongsu, the population either live on islands, semi-mobile floating cities, or in massive permanent underwater settlements, typically referred to as Yongwangguk. These are divided into 26 states as in the Jeobseoni government structure, though due to the mobile nature of the floating cities, and their size, some cities alone are considered states.

Cheongsu is home to a large amount of research facilities and high-tech development labs, and is widely considered the scientific capital of Yamatai. It also hosts the prestigious Cheongsu Galactic University, a public university open to all Humans, including those from outside of the Empire. Cheongsu also exports metals and exotic materials mined from the seabed, as well as pharmaceutical and biomedical products. Cheongsu is also home to the Cheongsu Abyssal Mirror, one of the most powerful telescopes in the Empire.

Floating cities
Main article: Floating city (Cheongsu)

The majority of Cheongsu's population lives in floating cities on the surface of the water. These cities are largely similar to floating platform settlements elsewhere in Yamatai, but are intended for large-scale, permanent inhabitation. To this end, the cities are equipped with high-tech equipment designed for self-sufficiency and even productivity comparable to land-based settlements. These include helical-bit drilling systems for dredging seabed for resources, water refineries, vertical farming, dynamic-flexible hulls, and other types of technologies developed on Cheongsu itself.

Floating cities are also able to grow themselves outwards over time without any external aid. The largest, Hyugeso, covers an area of 11,688 km², larger than some islands. Cities typically grow through adding continuous extensions or through connecting with other cities to form larger settlements. Life in the largest cities is almost identical to that of island or coastal settlements elsewhere. Economic activity is generally focused on fishing, deep-sea mining, fossil fuel extraction and seabed dredging. Cheongsuan floating cities are able to move through the use of thermohaline rudders, and smaller settlements regularly shift locations to avoid environmental hazards such as megastorms or detected Seomgoemul, or to locate new resources to exploit. The larger cities generally allow themselves to float on circuitous currents.

While most cities maintain anti-air and anti-space weaponry for defence, relying on their defensive forces for protection, a minority of cities are themselves heavily armed for naval combat as well, making these similar to the mobile floating fortresses of Yamatai.

Yongwangguk
Main article: Yongwangguk

Named after the undersea kingdoms of ancient Hanguk legend, Yongwangguk are large underwater settlements constructed on the sea beds. Typically taking the form of pressure-sealed biodome complexes in deep oceans or sprawling tube-connected structures in the shallow regions near islands, the yongwangguk complexes usually originate as extensions of island settlements or as deep-sea mining operations that eventually grew over the centuries. Over time, some of these isolated settlements have come up with a unique culture based around the scarcity of resources. They are highly crucial in producing the majority of Cheongsu's exported metals and rare materials, mined from the seabed. Yongwangguk complexes are also crucial in the continued study of the planet's undersea life and other types of scientific studies that require deep-ocean, high-pressure or isolated environments.

One particular underwater structure of note is the Hōrai underwater temple, the first of its kind. A sprawling shallow-water complex on the seabed near New Jejudo, Hōrai is a fully-contained Imperial Shrine temple that also includes residences for the staff and visiting pilgrims. Water-clearing technologies similar to that used in the Cheongsu Abyssal Mirror ensures that the water around the temple is crystal-clear at all times, allowing for the illusion of surrounding ocean life and underwater transports taking flight around the central dome.

Yongwangguk are also crucial in the practice of iso-meditation, whereby an individual uses a high-pressure diving suit and isolates themselves on the deep seabed without light or communications. This is said to allow for intense concentration and mental activity, and is also used in the training of the Dogsuli special forces.

Biodiversity
Jugeumyong are sea dragons.

Seomgoemul are a colossal naval creature that exhibits deep-sea gigantism on an epic scale. Scientists believe they may have survived underneath the ice pack during the last ice age, and the species as a whole may be billions of years old.