The origin of Koi-nobori is based on an old story that carp would grow to become dragons after ascending to heaven even in the rain, so samurai families flew the Koi-nobori in May, a rainy season, of the calendar of that time in hopes of the success of their son's careers in the Edo period.
鯉幟は、雨の中でもコイが天に昇って竜になることにあやかって、江戸時代に武士の子弟が出世できることを願い、梅雨の季節である当時の暦の5月(旧暦)に、掲げるものであった。