There is generally a limit into how opulent a world can become before it becomes absurd. Not only in wealth concentration but in what the wealth is used for. When it comes to Yakusoku, its small population of mostly wealthy nobles breaks every standard. In a civilization where post-scarcity is the standard, luxury would be something like having a fairly large plot of land on a planet rather than on some space habitat. For the inhabitants of Yakusoku, calling their life style "luxury" would be an insult.
An artificial operating as the capital of The State of Tenshi and located within Martial Space, Yakusoku is a shell world built around a small black hole. The body has a small population of 1.2 billion, however, these 1.2 billion people together have one of the highest concentrations of wealth on a single planet in the known universe, with an estimated 2 Septillion C-Units divided among these individuals.
The planet is entirely hollowed out, with a framework of active support holding the ten-kilometer-thick crust up over the core. Within the core itself lies many layers of radiation shielding and a black hole. The black hole itself has a small accretion disk which acts as a power source for the planet, its potential output rivaling that of its parent star. The planet has a surface area of 2.15 billion square kilometers and a radius of 64,000 km. Far larger than any natural terrestrial planet, Yakusoku has an absurdly low population density for its population at 0.48 people per square kilometer.
The large concentration of wealth on the planet warrants extra precautions. The nobles residing on the planet have vast numbers of ships stored in the system, capable of responding to a threat in minutes. They are designed to defend the planet long enough for the most important individuals to escape while allowing for a large fleet to eventually return to bolster the planet's already extensive defenses. A large portion of the energy of its star, Senta, is devoted to a high-energy laser array capable of vaporizing any covalent bond from over an astronomical unit away. Senta, a fairly small orange star, has been mostly converted into a Nicoll-Dyson beam.
The planet itself is covered in large nature preserves with flora and fauna. Numerous species once common on Aegyn before its collapse into chaos were only preserved on Yakusoku. For a time, its ecosystem was the only window researchers had into the life on Aegyn before archeological discoveries allowed for records of Aegyn's life to be uncovered.
Yakusoku has three major continents, Datte, Gerin, and Nepputsk accompanied by thousands of smaller islands. None of these continents were present when the body was first built. They were later created as land demand on the world grew. Without a magnetic field, a large array of orbiting magnetic field generators compensate.
The oceans are filled with artificially enhanced coral designed to live in not just shallow water but across most of the ocean floor, creating stunning reefs near the surface and equally stunning bioluminescent reefs towards the bottom. Large kelp forests fill more temperate areas of the sea floor.
The planet was first built in 1,038 BCE by the H. Aimer Corporation as a remote processing facility for the creation of Antimatter and Antimatter Weapons. Having secured a contract with the government of the Triumvirate Civilization, H. Aimer Corporation became one of the few private antimatter proprietors within Via Aylathiya. After the galaxy became increasingly turbulent due to the beginning of the deadly War of the Final Transition, much of the company's shareholders and executives fled to Yakusoku, the safest place they could. A sterile antimatter factory at the time, Yakusoku had only modest provisions for its new inhabitants.
When the Yohjan Confederacy collapsed in 0 CE, so too did H. Aimer Corporation, causing the entire star cluster to shatter into a large number of competing organizations. These organizations soon reorganized themselves into monarchies. On Yakusoku, four families organized themselves into noble organizations, the Takanashi Family, the Serebryakov Family, the Sakagami Family, and the Claes Family. These noble families were generally amicable to one another given the relatively small territory each one controlled. As the rest of the cluster fell into a nonstop series of wars, Yakusoku remained one of the few orderly areas of the cluster. In 2,304 CE, the four rulers of each family met together to formally unite their kingdoms into one state. They united themselves into the Tenshin Ministry. This ministry would go on to form the State of Tenshi.
Yakusoku soon became the capital of an expansive interstellar empire. The State of Tenshi united Kanadett in 4,012 CE, cementing Yakusoku as the political center of the star cluster. Using infrastructure left over from H. Aimer Corporation as well as weapons left over from the Triumvirate Civilization, Tenshi went on to become a great power capable of influence on a galactic scale, only earning Yakusoku an even more prestigious spot on the galactic stage. As Tenshi expanded, the infrastructure on Yakusoku, both defensive and civil, became some of the most advanced infrastructure in the galaxy. Other capital worlds within Tenshi, such as Ayomi and Hikari all had wormholes leading to Yakusoku.
The planet received minor damage from both the Great Empyreal Crusade and the War of the Ancients. Today it is a symbol of wealth and power in the State of Tenshi.