She was an imperial princess who transmigrated from ancient times to the modern world for the sake of her empire. She met him on her very first day and fell in love with him at first sight.
He was a young nobleman in modern society. By chance, he met her, and the moment he saw her, he fell in love at first sight.
Family grudges left him gravely wounded in a battle, and he died soon afterward. To bring him back to life, she sacrificed a thousand years of her essence.
When he awoke, he found himself in an unknown land, having lost the abilities he had possessed in his old world. From then on, he started at the very bottom of society, both to find her and to survive in this new world. Everything he did was for the two of them.