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.
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.
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.
Yang Chaoyue was known as a koi because every one of her lucky experiences seemed to fit the characteristics of the " lucky goddess." She won the first place in the competition not only because of her hard work and talent, but also because she received a lot of good luck. Her successful experience was seen by many as a symbol of "luck", so she was called Koi.
In 2019, the Koi King was a fictional character that appeared in some online novels. The Koi King was usually a character with strong luck and luck value. It could easily obtain all kinds of good luck and success. In real life, the Koi King didn't exist. Luck and luck value were a fictional concept that couldn't be realized in real life.