Boy's festival in Japan

子供の日

“Carp Streamers” (koinobori) 

a plenty of Koinobori in an event held in Tokyo tower

Today is "Children's day". It is also called "Boy's festival" comparing to Girl's festival on March 3.

Traditionally families having boys celebrate their boy's  healthy growth and happiness flying carp-shaped streamers(Koinobori) the exterior of the house or display dolls of warriors inside. I remember Koinobori flutter in the wind when I was a kid.

Koinobori imply a family consisted of father and mother, a boy.

the traditional style

History

Back to Edo-era, when a boy was born, warrior(samurai) families celebrate it putting a flag out at their home exteriors. This custom became common among the regular people.
And people connected this custom with a Chinese ancient story of  carp and started to display Koinobory.

The myth is like this.
There was a violent waterfall called the Dragon gate. Only a carp swam upstream strongly  to become a dragon while other fishes didn't make it.
People changed the custom and started to display Koinobori instead of flags. Koinobori symbolizes strength and success.

Less common

In the recent years more people live in apartments rather than houses.  They don't  have enough space to display Koinobori in the balconies. Even they do, Koinobori are flown by the strong wind and got stuck in ｔｈｅ balcony of .nextdoor.