Newly Discovered Hideyoshi Letter Sheds Light on Samurai Brothers

PUBLISHED 1 NOV 2026

New Evidence From 1585 Emerges

A newly discovered letter written by Toyotomi Hideyoshi has been authenticated by Osaka Castle, offering fresh insight into the relationship between one of Japan’s most powerful warlords and his younger brother, Toyotomi Hidenaga.

The document, dated 4 September 1585, will be displayed to the public for the first time as part of the special exhibition Siblings of the Warring States, running at Osaka Castle from 10 October to 23 November 2026.

Written under the name Hashiba Hideyoshi, the letter was addressed to Gamō Ujisato, a samurai lord based in Ise Province. In it, Hideyoshi confirmed that Yamato Province, corresponding broadly to modern-day Nara Prefecture, had been granted to Hidenaga following his military achievements during the pacification of Shikoku.

Hidenaga entered Yamato on 3 September 1585, accompanied by Hideyoshi and an army of approximately 5,000 men. The following day, Hideyoshi wrote to Ujisato from Kōriyama, outlining arrangements for the administration of the newly granted territory.

The letter reveals that Hideyoshi was personally involved in consolidating his brother’s authority. Among the matters addressed was the position of the Sawa and Akiyama clans, local samurai whose existing allegiance to Ujisato complicated the establishment of unified rule in Yamato. Hideyoshi instructed that they could either settle in Kōriyama and serve Hidenaga or move to Ise under Ujisato, allowing them a choice over their future.

The document therefore provides more than a record of a territorial appointment. It illustrates how political power, military service and personal relationships intersected during Japan’s turbulent Sengoku period. Hideyoshi’s decision to accompany his brother into Yamato, followed by his direct involvement in the region’s administration, suggests a close working relationship and a determination to support Hidenaga’s position.

Osaka Castle’s researchers examined the document’s vermilion seal, paper, handwriting and contents before concluding that it was an authentic Hideyoshi letter. Measuring approximately 14.3 by 86.4 centimetres, it is a previously unrecorded addition to the known body of Hideyoshi documents.

Around 7,000 documents attributed to Hideyoshi, including originals and copies, are known, making the discovery a valuable addition to the historical record.

The letter’s first public display forms part of an exhibition exploring the varied relationships between brothers and sisters in the Warring States period, when family alliances could prove decisive in securing a clan’s survival and prosperity.

For historians of the samurai era, this newly authenticated document offers a rare glimpse into the practical decisions behind the rise of the Toyotomi family — and the role Hideyoshi’s younger brother played in its growing power.