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.
I'm not sure specifically what 'cid kavin fanfic' is about as it could refer to various things. It might be a fan - made fictional story related to characters named Cid and Kavin. Maybe it's part of a particular fandom where fans create their own stories involving these two.
Since we have no background information on Cid, Daya and Shreya, we can also imagine that they are from different worlds. Cid could be from a working - class family, Daya from a wealthy family and Shreya from an artistic family. Their love story could be a complex journey of overcoming social differences, family expectations and personal insecurities. Cid's love for Shreya might be based on her free - spirited nature. Daya may be attracted to her beauty and talent. And Shreya might be looking for true understanding and acceptance in a relationship, which makes the whole love triangle full of twists and turns.
I'm not sure specifically what the 'cid daya marriage story' is as the term 'cid daya' is rather unclear. It could be a very specific story within a certain community, family, or cultural context that I'm not familiar with.
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.