Starry Sky Opener

Star Year 20,000, the 20,000th year since humans broke out of the solar system, humans have occupied most of the Milky Way. In the past 20,000 years, humans have found many ruins of pre-civilizations, but no one knows why the pre-civilizations disappeared. In order to find the answer, humans have expanded outward almost crazily. When the population is not enough to actually control the territory, the Opener Universe has come into being...