I'm not sure. It might have elements of reality, or it could be purely fictional. Without more context or specific knowledge about it, it's impossible to give a definite answer.
In such fanfics, Kyo might be depicted as strong - willed and passionate. Yuya could be shown as more easy - going yet with a hidden depth. Their relationship might be full of tension and attraction.
Koi was a very popular traditional cultural symbol, usually depicted as a fish with golden scales. In Chinese culture, koi represented good luck, wealth, and happiness. It was a symbol of many families and businesses. During festivals and celebrations, people would make koi ponds and release koi fish in hopes that they would bring good luck and happiness. Koi carp were also widely used in cooking and medicine. They were considered a kind of fish with magical effects.
I'm not sure specifically which'madam koi koi real story' you are referring to. There could be many stories with that name or something similar. It might be a local story, a personal anecdote, or something unique to a particular community.
Visual novels often have unique art styles and narratives. Since we only have the title 'koi hi koi fu en visual novel', it's difficult to determine the exact content. It might tell a story set in a particular cultural context, given the use of Japanese - like words. Maybe it's about different relationships and the emotional nuances within them, but this is all speculation.
During the pregnancy, they may rely on each other more. Kyo could support Misao during her mood swings, and Misao could help Kyo deal with his fears of becoming a father. This mutual support would strengthen their bond.