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 kevi fanfic' is about as it could be a very specific or niche fanfic. It might be related to characters named Cid and Kevi, perhaps their adventures, relationships, or some unique storylines created by a fan.