TOKYO, JUNE 29 -- In a ceremony of stark simplicity, with rituals and clothing harking back a millennium, Kiko Kawashima, a 23-year-old graduate student from an ordinary Japanese family, today married the second son of Japan's emperor.

As her family, government leaders and members of the imperial family watched from a distance, Kawashima and her college sweetheart, Prince Aya, 24, both clad in elaborate outfits and hairstyles of Japan's Heian Era (794-1185), silently entered a Shinto shrine on the leafy grounds of the imperial palace. They made offerings to the goddess of the imperial line and the prince recited wedding vows in archaic Japanese. After drinking sake from a special lacquer cup, they became prince and princess.

No music played, no one cheered, no rice was thrown and the bride and groom did not kiss. In fact they didn't seem to touch all day. Instead the couple -- the prince first, accompanied by a court attendant, and then his bride, a minute or so later, accompanied by a lady-in-waiting -- solemnly filed out to prepare for the other events in this ritual-filled day.

For Kiko-sama, as the adoring press here has dubbed her, the ceremony marked a dramatic transition from the world of the unassuming, middle-class family in which she was raised, to the cloistered, aristocratic world of the imperial court.

The Japanese clearly relished the idea that such a "Cinderella story," as one TV network put it, could occur. Millions watched the daylong television shows on the wedding and the couple; thousands lined their motorcade route home this afternoon. Young girls squealed in delight as they glimpsed the new princess, a diamond-studded tiara on her head, waving from a black limousine, looking not at all like the demure, young graduate student she had been only the day before.

Television cameras carefully monitored this transition to princess. Before dawn they staked out her parents' modest concrete-block apartment building on the Gakushuiin University campus to record Kiko's last moments as a commoner.

After arising at 4 a.m. and eating a final meal with her family, she emerged at 6:20 a.m., accompanied by an imperial messenger. Bowing to her brother and parents -- her father also shook her hand -- she set off for the palace. After performing purification rites she spent the next two hours dressing in the ancient imperial court wedding costume, a multilayered, colorful kimono weighing nearly 30 pounds and costing about $150,000. Her hair was tied back in a long mane and topped by a gold hair ornament.

Meanwhile, television cameras across town showed Prince Aya being sent off by his older brother, the crown prince; his sister; and his parents, Emperor Akihito and Empress Michiko, who by custom did not attend the marriage ceremony.

At 10 a.m., Aya, clad in a dark silk kimono decorated with a crane pattern used only by the imperial family, walked slowly to the Kashikodokoro, the shrine where the two were to be married. Behind him was a court attendant. After bowing he entered the shrine.

Then Kiko appeared, walking slowly and solemnly under the weight of her costume and accompanied by a lady-in-waiting, who scurried around to make sure the wedding kimono stayed in place. After bowing she entered the shrine. The 154 guests watched in silence.

A few minutes later the two emerged separately -- but married. They set off to pay their respects at other Shinto shrines in the same complex. The guests bowed to the shrine and quietly filed out.

By 3 p.m. Kiko's transformation into a princess was obvious to anyone watching the live television coverage. Arriving at the imperial palace for a first official reception with the emperor and empress, she wore a formal white gown with long white gloves, a diamond tiara, earrings and necklace. Across her dress was a sash signifying her new rank as a member of the First Class Order of the Precious Crown, the highest imperial honor for women. "Beautiful," gushed the television announcer. "She looks like a beautiful princess."

With the cameras rolling, the prince, now known by his official married name Akishino, formally reported the marriage and thanked his parents. "From now on the two of us together will fulfill our duty as imperial family members," he said in a barely audible voice.

"From now on I hope you will be happy and contribute to the nation, to society and to the people," his father replied. The empress wished the newlyweds "everlasting prosperity." The young couple then walked backward, so as not to offend the emperor and empress, until they reached individual tables set out with ceremonial foods to mark the marriage. Later, in a group photograph with the emperor and empress, Kiko and her prince appeared relaxed for the first time and smiled at each other.

By late afternoon the newlyweds set off in a slow motorcade for their new home, a small one-bedroom house in an imperial residential compound just a few kilometers from the palace. About 10,000 people watched the parade, with an almost equal number of police watching the people.

When they arrived home, the two bowed to staff and reporters before crossing the threshold, with the prince a few steps ahead, into their new life.

Tonight the couple had one more ancient marriage rite to perform: They were to eat boiled rice cakes from a rosewood box, saving some to bury in an auspicious place in the garden four days hence. The ritual is supposed to bring them many children.