I Just Transmigrated, and Now I'm About to Become a King of a Fallen Kingdom?

The good news: Murong An has transmigrated! He’s now the ruler of the Dark Shadow Dynasty, with a noble identity and exalted status! The bad news: Rebel forces have already stormed the capital. They could break into the palace and charge into the Dark Shadow Hall at any moment! I, cough, cough... Wait, what? I’ve only just transmigrated, and now the dynasty is on the brink of collapse? Am I about to become the ruler of a fallen kingdom? With a disastrous start from the very beginning, Murong An climbs the Star-Seizing Tower, ready to meet his death. Unexpectedly, the System for Building an Immortal Dynasty suddenly activates! [Host detected as having ascended the throne. Issuing ruler rewards... Congratulations, Host!] Obtained the Xuanyuan Sword! Obtained the Heavenly Mandate Dragon Armor! Obtained the Thunderwing White Tiger! I wear the Heavenly Mandate Dragon Armor, wield the Xuanyuan Sword, and ride the divine beast White Tiger. And you call me the ruler of a fallen kingdom? You’re asking for death! Years later, the immortals of the Immortal Realm stare in disbelief at the Immortal Dynasty, which has claimed numerous cultivation sanctuaries almost as soon as it ascended from the lower realm. A young-looking eunuch suddenly flies out from the dynasty, holding a list. He addresses the immortals in a solemn voice: “This is the Investiture of the Gods, created by the Celestial Emperor. If you make the list, you may take up an official post in the Heavenly Court and serve the Celestial Emperor...”