AT THE family home of Mr and Mrs Hisashi Owada in a quiet suburb of Tokyo recently, it was fish for breakfast and, one assumes, fish for lunch, tea and dinner. The day before, April 12 in the fifth year of the Heisei era (Emperor Akihito's reign), a man in morning dress had disembarked from a limousine with three gifts, presented to the family before a lacquered gold screen. The first consisted of five bolts ofsilk, between them worth JPY3 million (HK$216,000), each bearing a symbolic pattern chosen by the empress: ''Mankind'', ''Black Bamboo'', ''Arrays of Mountains'', ''Moments of Musical Joy'' and ''Shining Silk of Birds of Good Luck''. The second was a case of sake, symbolising celebration. The last was a pair of large Red Sea bream, one male and one female, an emblem of happiness. The kimono-clad recipient of the gifts, the Owada's 29-year-old daughter, Masako, bowed as the court official explained the significance of each of the presents and replied: ''I accept them in awe.'' The ceremony, Nosai-no-Gi (Rite of Betrothal), was over in moments, and the Imperial emissary departed to the crown prince's residence to announce what the rest of the world had known since January: after a decade of anxious waiting, 33-year-old Prince Naruhito, heir to the Chrysanthemum Throne, was getting married. The engagement, confirmed so elegantly with the bestowal of the bream, began unofficially in mid-December when, after six years of nervous wooing and several polite refusals, Ms Owada finally agreed to give up her brilliant diplomatic career to marry Japan's next emperor. The news, leaked a month later, provoked a frenzy of excitement. There were the familiar reactions, common to royal marriages everywhere - picture specials, interviews and biographical rundowns (revealing, among much else, that the future empress once earned the nickname ''Slugger'' for her skill at softball). Within days, dolls of the happy duo, and reproductions of His ties and Her scarves, were rushed out by grateful merchandisers; one entrepreneur even devised a dish of ''Masako noodles'', featuring corn, special seasoning (''sweet and hot'') and a sprinkling of gold dust. Beneath the trivia, however, other emotions were discernible: a near-unanimous popular approval, and the hope that change was coming. Members of the Imperial Family are remote figures, rarely emerging from Tokyo's Imperial Palace, and never evading the stern mediation of the fearsomely traditional Household Agency. Ms Owada seemed a breath of fresh air. Like the crown prince's mother, Empress Michiko, she is a commoner and exceptionally gifted, with degrees from Harvard and Tokyo universities, and six years of experience as a translator and negotiator in the foreign ministry. A distant scandal, involving a relative employed by a discredited chemical company, had led the Household Agency to drop her name from a list of suitable candidates. She, in any case, was not interested. But, on her return from a stint in Oxford (with more letters after her name), the prince renewed the assault, and eventually she gave in. It seemed the happiest of endings. The affair was presented as an untraditional triumph of considered choice over bureaucracy, of the dashing young couple over the Imperial mandarins, although the Asahi Shimbun newspaper added a note of caution. ''If she ends up politely smiling 'royal smiles', the crown prince's choice of bride will not have been put to good use,'' it warned. Perhaps these are early days. But, for the past three months, polite smiles are about all Japan has seen of the soon-to-be-princess. The fish-giving was one of a series of elaborately stage-managed encounters before the enactment of the Shinto marriage rite today. Things began in earnest in March when Ms Owada began ''princess training'', 62 hours of private lectures by a roster of elderly academics and ritualists. Ms Owada has studied waka, the 31-syllable poems with which the Imperial Family amuse one another on ceremonial occasions. She has improved her Imperial history and Japanese calligraphy. Above all, she has been tutored in the countless protocols which will determine the rest of her life: when and how deeply to bow (15 to the commoners, 45 to the emperor); how to walk (never in front of her husband); what to wear (nothing that will outshine the empress). Meanwhile, the ancient rites accumulate. Recently, Ms Owada was able to put her waka skills into practice when she and her finance exchanged romantic poems in classical Japanese and the next day another Imperial messenger dropped in to enact Kokki-ro-Gi,the official notification of the date of the nuptials. At 9 am today, she will appear at the Kashiko-dokoro (awe-inspiring place), one of three private Shinto shrines within the palace. Clad, respectively, in an orange robe, and a 15-kilogram, 12-layered silk kimono, the crown prince and his bride will enterthe sanctum, dedicated to the sun goddess, Amaterasu Omikami, who (until the late Emperor Hirohito renounced his divinity in 1945) was considered to be the direct ancestor of the Imperial Family. There, speaking in an ancient courtly dialect, incomprehensible to most Japanese, he will announce his marriage in the shade of his forebears. After a simple exchange of vows, the couple will toast one another with cups of sake. Late in the month, they will be whisked to Ise Shrine, the holiest site of the Shinto religion, for further ceremonies. A series of glorified tea parties will be held for friends and favoured members of the diplomatic and political communities. There will be no guest list of foreign heads of state, no horse-drawn coaches or Imperial walkabouts. By the standards of royal extravaganzas worldwide, the marriage will be a closed affair, conducted in an invisible palace, behind a moat, behind stone walls. In one sense, Ms Owada Masako has much to be thankful for. The emperor's mother, Nagako, 90, was kept under virtual house arrest during her seven-year engagement to Hirohito. The crown prince and his siblings were the first Imperial babies not to be nourished by wet nurses and to live with their parents rather than being farmed out to guardians. On the other hand, given that this was the 1960s, it would be hard to see how tradition could have conceded less. Ms Owada's own assessment of her chances is perhaps hinted at in a card which she sent to her parents in December, a few days after making her decision. Surprisingly perhaps, it was released by the Imperial Household Agency. These may turn out to the last uncensored words of Masako Owada that will ever be made public. ''Dear Father and Mother,'' she wrote. ''This Christmas may be the last we'll be able to spend together. I really appreciate that you raised me in such a warm and happy family. Tough times are waiting for us, but I hope we get through. Sincerely, Masako.''