Apocalypse: Sci-Fi Heavenly Court

An alien civilisation comes at Earth in force. Cities fall, and human civilisation is close to being finished off entirely. Chen Feng lives through all of it and dies with it, then wakes up carrying the memory of everything that is about to happen, at a point early enough to do something. He starts the Southern Gate project alone. Using technology that has not been invented yet in this timeline, he builds a heavenly court in the sky, a fortress and command platform holding weapons and a system of powers nothing on the planet can currently match. The first job is holding the line at home, keeping the invasion off the Blue Planet and sheltering what is left of the human population behind the court's guns. From there he pushes outward. The court becomes the base he works from as he moves past Earth's orbit and out of the galaxy, taking the fight to the territory the invaders came from and putting down the threats waiting further out among the stars.