Yui is an e-class moon orbiting the planet Cardinal in the Milky Way Galaxy galaxy. The moon is in the Akihiko system which is under the control of the Confederacy of Borealis. The moon is home to an offshoot of the Takanashi Family called the "Dia-Takanashis" as well as the headquarters of Dialapse.
The moon has a small population of only several million people. All of which are a part of the high-level operation of the company.
The moon is covered in various islands, the largest of which being comparable to Brazil, and the smallest of which are the size of the Vatican. Every island has a use and was placed mostly intentionally to make the environment appear natural, but also aesthetically pleasing.
Most of the islands have houses or cabins on them for some of the top officials of the Family. Those that have less power live on the central island called "Senta." While living in relatively "cramped" conditions on this large island, they still each have about four square kilometers to themselves. As the population grows, lower-level individuals that are merely employees rather than family members live in apartments on Senta or in orbital infrastructure.
Yui orbits a star about twice as massive and over 2000 degrees hotter than Sol. As such, the different wavelengths given off by that star prevent green plants from thriving. The plants were custom tailored to resemble Earth plants while using purple pigments rather than green ones.
Other than that, the biology there is very similar to that of earth. They have adapted to live on the low gravity, but since it has't been long, they aren't much different. Flying species have changed the most, generally growing smaller wings and heavier bodies. Insects especially have grown to have much smaller wings to allow for easier burrowing and faster metamorphosis.
The Akihiko System
The Main star of the system, named Akihiko in honor of one of the major scientists working on creating the antimatter production still used widely to this day.
There is only one planet in the Akihiko system named "Cardinal." It was a name chosen on a whim when the CEO was asked what the name of the gas giant was. Before it was named, everyone just referred to it as "The Gas Giant" or "The Giant." The planet has large amounts of methane and ammonia in addition to it's large amount of hydrogen and helium. These gases in the atmosphere act as a major source of fuel and materials for the planet and even Dialapse itself.
Cardinal is a temperate ice mega-giant rather than just a pure gas giant.
The moon used to be surrounded by hundreds of other moons and small asteroids captured by it's parent. All of those moons have since been mined out for materials or otherwise removed from the system to minimize the risk of impacts with Yui.
Yui was first colonized in 72678 by the Takanashi Family. It was designed to be the headquarters of Dialapse since the very beginning. However, it was also built to house meetings and aliens so that the Family could meet with individuals without having to let them into the Kanadett.