On Oct. 26, 1984, Riki Kato read an article on the front page of the Hokkaido Shimbun that would change his life and send him in pursuit of a historical mystery that now spans four decades.

The newspaper, for which Kato worked as a reporter at the time, announced that day that 11 portraits of Ainu chieftains, completed in 1790 by the artist Hakyo Kakizaki, had been discovered in storage at the Museum of Fine Arts and Archaeology in Besancon, France. There were originally 12 paintings in the original set, collectively known as the “Ishu Retsuzo,” but one had disappeared.

How the silk paintings, each measuring 45.5 by 36 centimeters, ended up in a small French town nearly 10,000 kilometers from Hokkaido was not explained in the article.