These are flown in Japan on May 5 (Children's day holiday).

Japanese carp streamers were developed mid 18th century in Edo era to celebrate birth of son. The design was inspired by a Chinese legend that a strong carp can become a dragon if it goes up a waterfall. Parents wished their son would become a strong man like a carp going up falls.
Nozomi Kariyasu, 4 September 2000