In the past year, rediscovered women painters, photographers, textile artists, and botanical illustrators have been lifted from dusty storage into gleaming gallery spaces in London, New York, Toronto, and Sydney. But Japan’s Katsushika Oi is not among them. The third daughter of the printmaker Katsushika Hokusai was his amanuensis, managed his affairs, and was by his own admission the better painter. And although she probably wielded the brush in many of the late, great works attributed to him, full recognition still eludes her.

There are the lost women artists who worked in obscurity – like Vivian Maier, the Chicago nanny-photographer whose 100,000 images were discovered in a storage locker. Many others were known in their time but posthumously dropped from the canon. Katsushika Oi is one of the latter. Oh-ee, her art name, was said to be a play on her father’s frequent summons ‘Hey, you!’, but more likely meant ‘loyal to Iitsu’. Iitsu was one of her father’s many art names. Born in Edo around 1800, when Hokusai was 40, she worked in his North Star Studio making ukiyo-e woodcuts, paintings, and illustrated books from childhood until he died in 1849. By then Oi had ‘achieved a certain degree of fame in Edo’, wrote Patricia Fister, in her catalogue Japanese Women Artists, 1600-1900. But after 1853, when Admiral Perry and his black ships ‘opened’ Japan, the studio and the country fell into turmoil. One day, according to words left by her niece, Oi set off with her brushes in her sleeve to see about doing a painting for a man called Bunzo at the inn at Totsuka. She was never seen again.

For decades, debate about Oi’s role in the enormous Hokusai oeuvre has percolated among art museums and historians. Common sense would indicate that it is impossible that the 80 works dated within the last few months of his life could have been completed in that time by a nearsighted nonagenarian whose palsy had returned. But common sense does not dictate. Mythmaking does.

The earliest image known to be by Oi is Sailboats on a Misty Day (now held by the British Museum), brushed for a kyoka club publication at age 10. Maturing, Oi proved to be the most talented of three daughters. She married an art student, separated from him when her mother died and returned to her father, where she lived until he reached the amazing age of 90. Average life expectancy at the time was 45.

Little was written about the chonin (townspeople) or its artists in their time. But the woodcuts themselves offer a wealth of visual information about Oi’s world – the flimsy tenements, street vendors, workers, banquets, actors, festivals, bridges. Scholars describe the repressive Tokugawa regime, its censors and punishments. The ‘floating world’, of whose women Oi left her most enduring images, was long glamourised and prettified. But it was in fact a locked and disease-filled slave ghetto into which young girls were sold to be worked as ‘courtesans’ – prostitutes in stylish clothes – into an early grave.

A couple of sketches depict Oi. She is the downcast, idle woman seated beside Hokusai in a sketch of the master created 50 years after his death. More accurate is the other, on what appears to be a receipt for services. It gives more equal billing: cartoons of both her and her father’s face. She has a broad jaw and pointed chin and a Buddhist mark in the centre of her forehead. In several random accounts that do exist, Oi is described as not beautiful, childless, ‘masculine’. Her chin was too big. She ‘was not trained to be a wife’; she ‘paints but does not sew’; she kept no kitchen and fed her dad on store-bought food. Certain of her contemporaries add that she was a supremely talented painter ‘in her own right’. One states that the works of Hokusai’s ‘Iitsu’ period are by Oi. And her father notably said she painted ‘beauties’ better than he could.

Today, only 10 works can be definitively attributed to Oi. These include the painted silk scroll Three Women Playing Musical Instruments in the Museum of Fine Arts Boston, Guanyin’s Arm at Cleveland Museum of Art, and Display Room in the Yoshiwara with women lined up as merchandise. Its dramatic shadows, atypical of the period, are one of Oi’s innovations. These pictures show her exceedingly fine technique, dense colours, trademark long tapering fingers and various compositional tropes. The last work for which she was celebrated is the illustrated book Onna Chohoki (Treasury of Education for Women). During and after her father’s lifetime, Oi took her own commissions and had her own pupils. Receipts show that Oi was commissioned to create the work ‘Chrysanthemums’ and paid more than her father was during his lifetime. But the daughter who maintained Hokusai’s studio through his decade-long bout of ‘the palsy’ and its later return, and outlived him to walk in his funeral procession, cannot escape his shadow.

Circumstances contributed: political collapse; the coming of foreign ways and foreign traders, no matter how well intentioned; and the international market and enthusiasm for Japonisme. Hokusai père was becoming a sensation in France. As the scholar Julie Nelson Davis has written, Oi and Hokusai were in partnership. The reality is that any works – including the monumental The Great Wave – could just as easily have come from her brush as from his. But it was expedient to credit the master.

Verification of Hokusai works is uncommonly complicated. There were students, and there was Oi, who had perhaps acted as his brush many years previously. Fifty years after his death, Hokusai was famous enough that the French wanted his life story. His former student Iijima wrote a biography, and characterised Oi as a droopy sidekick, an image that has stuck. An unsigned sketch of Hokusai setting out on his travels, by Oi, was placed on the cover. It is now found in the Musée Guimet as Hokusai’s self-portrait. Stories of forgers at work both during and after Hokusai’s life still linger in Obuse, Nagano, the mountain town he and his daughter fled to while under threat from the Tokugawa. A local citizen has a storeroom containing lily sketch by Oi, as well as teaching materials and what could be the practice signatures of a forger.

The last years of Oi’s life and the fate of the artworks of The North Star Studio are another mystery. Oi’s secret is to some extent the secret of Hokusai himself. After his death, disciples vied for control of the studio. Certain apprentices went to Yokohama to paint pictures for export. Oi may have followed. Local lore repeated by Shinya Ichikawa and Makiko Koike, curators of Isago no Sato Museum in Kawasaki, suggest she may have been attacked by highwaymen and killed in this chaotic time. But they also find it futile to try to separate out the two artists’ work. Father and daughter worked as a team.

Many art historians do not agree. The default position for unsigned works is to assign them to Hokusai alone. While it is noted that there are two very different styles in the complete oeuvre, academics counter that Hokusai’s is ‘the style of all styles’. The MFA Boston’s 2023 ‘Hokusai: Inspiration and Influence’ included works by Oi but saw her in the same context as other students. The museum is still unpacking William Sturgis Bigelow’s 1911 donation of 40,000 works of Japanese art. It was Bigelow who acquired Oi’s superb, signed painting Women Playing Musical Instruments, but left no record where he got it.

Oi’s connections to American collectors are slight, but tantalising. In 1879 Edward Morse, an American scientist living in Japan, wrote of being ‘given’ Hokusai works by ‘an old gentleman, who had for a long time treasured these precious objects’. The man, who is not named, claimed to have been among the last of Hokusai’s pupils, and that the master painted the hanging scroll (on silk) when he was 86, without glasses. An interesting sidenote is that, in 1848 – Hokusai’s last year, the civic administrator Saito Gesshin in his Chronology of Edo, wrote of the old man, ‘When he draws he uses spectacles over his eyes.’ It may seem a small point but in the context of the eighty superbly detailed works dated in his final few months of life, it seems relevant.

Morse goes on: ‘A daughter of Hokusai inherited in some degree the genius of her father, as shown by some drawings of flowers and women now in my possession.’ About those sketches he observed that they had no signature or seal and that the kakemono was ‘very rich and beautiful in colour.’ (red, green and grey) At least one of these, Empress Jingu, was donated by Morse to the Metropolitan Museum of Art in New York. In the 2023 publication Late Hokusai from the British Museum Press, the Met curator Dr. John Carpenter joins Kobayashi Tadashi in seeing the work as Oi’s. It is unsigned.

The last of the three Bostonian aficionados of Japanese art was Ernest Fenollosa, whose 1900 catalogue of ukiyo-e works held at Ueno Park in Tokyo attributes several paintings to Oi. However these attributions disappeared by the time the collection reached Boston.

Many factors worked together to lead to Katsushika Oi’s disappearance. In life her signature was discouraged. Chroniclers labelled her as unfeminine, unpleasant. Regime change shook her world. Local knowledge that conflicted with a rising mythology of the master Hokusai was disregarded. Collectors from other cultures weighed in and favoured the male master. Catalogues were ‘corrected’. A century and a half later, the situation is difficult to rectify. Museums defend their pricey holdings. In the search for attribution, art historians demand a rigorous proof that is likely not attainable in the case of women or those not in a position of power.

But curiously, Oi has not disappeared. Far from it. Her own mythology has made her beloved in Japan. She may have been a witch. She collected mushrooms, hoping for eternal life. She practised physiognomy. She drank and smoked like a man; she spoke forthrightly but was a dutiful daughter. There have been novels, manga, an anime, and a television series made about Oi. A new feature film got bad reviews: the actor portraying Oi was too pretty. It seems the Japanese love her for her eccentricity and for persevering from the very shadows she painted.