The plot could center around the king's character development. He might start as a young and inexperienced ruler and face numerous obstacles. These could include external threats from neighboring kingdoms or internal unrest among his people. As the story progresses, he may learn important lessons about leadership, justice, and sacrifice. There could also be a love interest for the king, which adds another layer of complexity to the story. The 'eternal' aspect might suggest that his rule has a significance that spans across different eras or dimensions in the fictional universe of the novel.