Well, Cid Kagenou does reveal himself at a crucial point in the manga. This reveal has significant implications for the plot and character development.
I don't have a definite answer for you. The manga might be keeping us in suspense about who Cid Kagenou will end up with. It could be a surprise twist or a character that has been hinted at throughout the series.
Writing or seeking fanfic involving such inappropriate and non - consensual or inappropriate pairings is unethical and goes against the values of most fandoms. So, no, there should not be any such fanfics.
A great topic could be Cid's adventures in a new land. He could be exploring uncharted territories, facing new monsters, and making new friends along the way. This would focus on his character development and his skills as an adventurer.
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.
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.