It's about a world that has been thrown into ruin. There are complex characters and a unique plot. It likely involves themes of destruction, survival, and perhaps some sort of power struggle.
I'm not sure exactly, but usually in such a story, there would be a protagonist who is likely to be at the center of the action, trying to deal with the ruined kingdom situation.
I don't think so. Reading the manga can enhance your understanding and appreciation of the anime. You might notice things you missed before or gain a deeper connection with the story and characters.