It's hard to say. Sometimes the manga keeps such revelations hidden until the right moment to create suspense. So, we'll just have to wait and see if Rose discovers Cid's secret identity.
Their relationship can be developed through shared adventures. For example, if they go on a quest together to retrieve a powerful artifact. During this journey, they have to rely on each other's skills. Cid's combat and strategic skills combined with Rose's knowledge of the local area or certain magic can bring them closer. They start to respect each other more, which is the first step in developing their relationship.
The main character is Cid. He has this interesting dual - life kind of situation. Then there's also Beta from Shadow Garden. She is often involved in the group's operations and has a connection to Cid as well. And we can't forget about the various antagonists that they face which also play a role in shaping the story.
One thing that makes the 'Shadow Garden light novel' interesting is its characters. They are well - developed with their own motives and backstories. Also, the world - building is great. There are different factions and power dynamics at play. The story also has a good amount of plot twists that keep readers hooked.
One plot idea could be that Rose discovers Cid's true power in a moment of crisis. For example, when facing a powerful enemy that the Shadow Garden can't easily defeat, Cid reveals his real capabilities to save Rose and the others. Another idea is a love triangle where Rose has feelings for Cid, but Cid is so focused on his shadowy plans that he doesn't notice at first, while another character also vies for Rose's attention.
Well, El Cid has a basis in history. Rodrigo D铆az de Vivar was a real person, but the stories about him have likely incorporated fictional elements over time to make them more captivating.