May 5 is Children's Day in Japan. It's a national holiday during the Golden Week period. Until recently, May 5 was known as Boy's Day-- a day for all the little guys. Girls had their own holiday, too. For Boy's Day, it was and still is common to hang carp streamers and display samurai dolls or armor. The carp is a symbol of success, hence the significance of hanging the streamers. Displays of samurai dolls or miniature samurai weapons and armor is a time-honored tradition that symbolizes that boys will grow up to be strong warriors.
This life-sized and full set of late Heian/Kamakura period replica armor was on display in the lobby of the Okura Hotel in Kyoto to commemorate Children's Day.