Koinobori. Carp streamers, known as "koinobori" in Japanese, decorate the landscape from April through early May, in honor of Children's Day on May 5. In Japanese culture, the carp symbolizes courage and strength because of its ability to swim up a waterfall. Since these are traits desired in boys, families traditionally flew koinobori from their homes to honor their sons. Ranging in size from about a foot to several meters in length, the koinobori resemble jewel-toned sea beasts swimming through the watery, azure skies. May, 1998.