Underground Starry Sky

While sleeping peacefully, a person's soul was split in two. One half remained on Earth, living in a daze, while the other went to a parallel world of Earth. But something went wrong after it arrived, and he regained his memories. From then on, he began a journey to return to Earth. Along the way, at someone else's behest, he unified the continent of another world, and then set out on an expedition to Earth.