From the wiki: “Hinamatsuri [Doll’s Day, or Girls’ Day] is celebrated each year on March 3. Platforms covered with a red carpet are used to display a set of ornamental dolls [hina-ningyō] representing the Emperor, Empress, attendants, and musicians in traditional court dress of the Heian period. The custom of displaying dolls began during the Heian period, tracing its origins to an ancient Japanese custom called hina-nagashi [doll floating], in which straw hina dolls are set afloat on a boat and sent down a river to the sea, supposedly taking troubles or bad spirits with them.
“The term for the platform in Japanese is hina dan; the layer of covering is called dankake or hi-mōsen, a red carpet with rainbow stripes at the bottom. Families generally start to display the dolls in February and take them down immediately after the festival. Superstition says that leaving the dolls past March 4 will result in a late marriage for the daughter.”