Koi fish have been a very profound part of the Japanese psyche for thousands of years. Even nowadays there is hardly a temple that does not have a small koi pond dense with these majestic fish. The novel lore possibly came from China but has been handed down for so many thousands of years that Japanese now that think that it is ever been there respective. Anyway the koi fish is think to be a strong, powerful and independent fish.
The story goes that this fish swims up stream against the recent (thus is why there are frequently drawing splashing) and if they are powerful sufficient and have sufficient power they ultimately reach the maximum gate and once they pass through it they become a dragon and fly up powerfully into the sky.
The symbolism for most Japanese is one of potency, power and being true to one self. This is anything that works well with many women nowadays who want to strike out on their respective and feel their respective power and freedom.