During the Muromachi period (14th–16th century), the Sō clan, who oversaw the domain and island of Tsushima, played an important role in facilitating trade and diplomatic relations between Japan and the Korean kingdom of Joseon. By the Edo period (17th–19th century), however, the clan had come to monopolize this window of interaction, acting as the Tokugawa shogunate’s official and only mouthpiece to the Joseon kingdom. The massive amounts of diplomatic documents collected throughout the years have been stored in an archive in Banshōin, the ancestral temple of the Sō clan. Of these, 14,033 items are now in the Kyushu National Museum collection. Correspondences to and from the officials of the Edo shogunate make up most of the collection, which also includes valuable historical documents recording the state of Japan-Korea diplomatic relations from the Muromachi period onward.
Some of the most intriguing items in this collection include a number of copper seals known as tosho, which were granted by the Joseon government to Japanese travelers to be stamped onto diplomatic documents. Interestingly, most of the seals in the Sō clan archives have names of people from outside Tsushima, showing us how the clan had made it a point to gather as many trading permissions as they could from off-Tsushima figures on the island. The clan had even created wooden forgeries, such as of the tokuyūrin 徳有隣 seal representing the Ashikaga shogunate clan, and the royal wijeong’ideok 為政以徳 seal of the Joseon king, with which they falsified documents from both nations. These show the unique position that the clan had carved out for itself within the scope of Japan-Korea diplomatic relations up to the early Edo period.
Another item of note is a ginseng root bearing an uncanny resemblance to the shape of a human body. This root was discovered by an advisor to the Tsushima domain and presented to the Sō clan head in 1713. During the Edo period, the Tsushima domain monopolized the market on importing ginseng from Joseon. While most of these imports would have been sold or otherwise consumed, this root was retained and treated as a rarity for its peculiar shape. The collection also comes with forty-five boxes of miscellaneous documents.