Yes, there are many. For example, there are fanfictions about character relationships in a platonic way, like how two characters from a series become best friends and support each other through difficult times.
There is no scientific evidence to suggest that the penis experiences significant growth during sex. The size of the penis is mainly determined by genetics, hormones during puberty, and overall health.
A 'surprise cock growth story' could potentially refer to unexpected growth in roosters. In a farming context, sometimes a young rooster might seem to have a sudden growth spurt. This could be due to better nutrition, a change in living conditions like more space to move around, or just its natural genetic development kicking in at a certain stage.
One common misconception is that frequent sex can lead to penis growth. As I mentioned before, this is not true. Another is that certain sexual techniques or positions can cause growth, which has no scientific basis.
No, it's not popular. Popular fanfiction tends to revolve around well - established characters and common themes that many fans can relate to. This 'big cock growth percy fanfiction' with its rather strange - sounding concept is not something that would appeal to a large number of people. It's more likely to be a very niche creation that only a small number of people might be interested in, if any at all.
In the animal kingdom, male deer grow large antlers. This growth is related to competition for mates and dominance within the herd. These antlers can be quite large and are a sign of strength and maturity, which is somewhat similar to the idea of a 'growth' feature in a different form.
I'm not aware of any widely known 'furry cock growth stories' in mainstream media. The furry fandom has a vast range of stories, but this specific concept doesn't seem to be a common, well - known theme.
There may be some stories in the field of veterinary medicine that could be considered as 'surprise cock growth stories'. For example, a rooster that had an illness or injury that was expected to stunt its growth, but instead, it recovered and grew in a way that surprised the veterinarians. This could be due to new treatments being effective or the rooster's own strong immune system defying the odds.