The Japanese Doll Festival (雛祭り ,Hina-matsuri), or Girls’ Day, is held on March 3, the third day of the third month. Platforms with a red hi-mōsen are used to display a set of ornamental dolls (雛人形 ,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. Formerly, people believed the dolls possessed the power to contain bad spirits. Hinamatsuri traces its origins to an ancient Japanese custom called hina-nagashi (雛流し, lit. “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 Shimogamo Shrine (part of the Kamo Shrine complex in Kyoto) celebrates the Nagashibina by floating these dolls between the Takano and Kamo Rivers to pray for the safety of children. Also people have stopped doing this now because of fishermen catching the dolls in their nets. They now send them out in to the sea, and when the spectators are gone they take the boats out of the water and bring them back to the temple and burn them.
The customary drink for the festival is amazake, a sweet, non-alcoholic version of sake made from fermented rice; the customary food is colored arare, bite-sized crackers flavored with soy sauce. Chirashizushi (sushi rice flavored with sugar, vinegar, topped with raw fish and a variety of ingredients) is often eaten. A soy sauce-based soup is also served containing clams still in the shell. Clam shells in food are deemed the symbol of a united and peaceful couple, because a pair of clam shells fits perfectly, and no pair but the orignal pair can do so. (Source)