Originally, this festival was anything but a children's party. Its roots go back to a Chinese purification ceremony that was held on the third day of the third month on a riverbank. In the Heian-period (794-1185), this rite was also introduced to the Japanese court. Under the guidance of exorcists, courtiers would transfer their impurities to human figures made of paper by rubbing these against their own bodies. These figures, called katashiro or hitogata - and in fact literally "scapegoats" -, would then be thrown into the river, to be carried off by the stream...
This custom still exists in Japan, but not anymore on March 3 - it is now performed in shrines all over the country at the so-called nagoshi purification in summer (except for the Shimogamo Shrine in Kyoto, which still holds a nagashi-hina rite in the morning of March 3).
Why the peaches? Not so much because the peach may be in bloom around this time, but rather because in ancient Japan peaches were also used to exorcise evil - they were thought to have strong magic powers, as in the scene of Izanagi, the Creator Deity, who when fleeing from the Underworld, throws peaches at the evil hags pursuing him.
Back to the Girl's Festival. The Hina dolls presumably developed from the human figures thrown into the river - perhaps at some time children started to make clay figures and dress these up and gradually the religious significance was forgotten - the emphasis shifted to enjoying the beautiful dolls. The festival received its present form in the Edo-period (1600-1868), when parents began to use this occasion to pray for the future happiness in marriage of their young daughters.
Hina dolls are not ordinary dolls, but ceremonial dolls, a heritage of the family, sometimes handed down for generations. They are only taken out for the Doll's Festival and carefully kept in boxes during the rest of the year. They are usually put out in the second or third week of February and immediately taken away again the day after the Hina Matsuri. The classical way of display is on five or more tiered steps covered with bright red cloth.
[Seven-tiered Hina doll set. Photo Wikipedia.]
On the top platform go the Emperor and Empress, also called (O-)Dairi-sama or "Obina and Mebina" - the Emperor sits to the left of the Empress. They wear resplendent court costumes of silk, remniscent of the Heian-period. The robe of the Empress is called the "juni-hitoe" (twelve-layered ceremonial robe).
The second tier is occupied by three court ladies carrying sake holders (sannin kanjo), the third one by five male musicians (gonin-bayashi) with drums and flute; one is a singer.
The Minister of the Right (Udaijin) and the Minister of the Left (Sadaijin) usually sit on the fourth tier. As the Minister of the Left was higher in rank, he has a long white beard to indicate wisdom. On the fifth tier we often find the Mandarin Tree of the Right (Ukon no Tachibana) and the Cherry Tree of the Left (Sakon no Sakura) plus three guards or escorts - these trees are also planted in front of the Hall of State of the Imperial Palace.
On the lowest tiers several miniature household articles are placed, such as a chest of drawers, a palanquin, a dinner set, musical instruments, and other exquisitely made, tiny artifacts. Usually peach blossoms are also among the decorations of the stand.
A set of Hina dolls is extremely expensive - expect to fork out several hundreds of thousands of yen for a full, classical set. But as it takes up a lot of space which Japanese homes usually do not have, a shortened version of only the Emperor and Empress is often put up nowadays.