Japan was first visited by Antonio da Mota, a Portuguese explorer, in 1542. From that time until 1614 when Shogun Ieyasu ordered all Christian missionaries to leave Japan, there was significant contact with Japan adopting European ideas. For example, muskets were being mass-produced locally by the 1560s. Interestingly, according to
Wikipedia “Organized open-boat shore whaling began in the 1570s”. However, this remained coastal. By contrast, Basque whalers established bases in
Labrador from at least 1536 and were also involved around Spitsbergen from 1612. Thus the Basques could process whales and transport the products economically over long distances. My suggestion is that someone (Spanish?) realizes that there are many whales in the North Pacific and has the idea of setting up a base north of Japan (the Kurils?) and selling the whale oil to Japan around 1550-60. Then, we can imagine that the Japanese learn the techniques and that Ieyasu allows whaling and voyages to the north to continue when he imposes his seclusion policy on contact with the Christian nations.