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.
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.
We often call lucky people koi, but in fact, koi are not constellations but mythical creatures. According to legend, koi were creatures with good luck and longevity that could bring luck and blessings to people.
Astrology did not explicitly mention the connection between astrological signs and good luck. On the contrary, constellations were more used to study people's personality, characteristics, fate, and other factors.
Therefore, no constellation was a real Koi constellation. Good luck depended on one's efforts and actions, as well as the living environment and opportunities.
There's no way to tell who made the 'koi new story' just from this name. It could be an individual writer, a group of storytellers, or even a company. We would need more details like where it was first published or what medium it's in to start figuring out who the creator might be.