(The Japan Forum)
Putting up koinobori, or streamers in the shape of carp, is a spring tradition in Japan. Colorful cloth carps flying against the blue sky can be seen across Japan from the end of April until May 5, Children's Day.
The tradition is said to have begun in the Edo period (1603-1868) based on a Chinese legend about a strong, brave carp swimming upstream and becoming a dragon. Along with the Momo no Sekku (Peach Festival) for girls, which was celebrated on March 3 in the old lunar calendar, the Tango no Sekku (Tango Festival) for boys was celebrated on May 5. This festival is now known as Children's Day. By putting up carp-shaped streamers made of cloth and other material in their gardens, families announced the birth of a boy and wished for his healthy growth.
Koinobori have gradually changed over time. Originally made only in black, other colors like red and blue were added, and baby carps are now flown with the larger ones to symbolize the family. Today koinobori are a colorful sight, with wind wheels at the top of the pole and a five-colored streamer above the carps.
There is a famous Japanese children's song about koinobori flying higher than the roof. Nowadays cities are full of multi-story apartment buildings, and the sight described in the song has become less common. But the streamers can still be seen all over Japan, as smallerones are available for apartment balconies.