In a letter sent to Munakata Saikaku with his “kao” stylized signature, Toyotomi Hideyoshi praises her achievements in the battle against the Shimazu clan. (Kunihiko Imai)

TARAGI, Kumamoto Prefecture--The traditional notion that only men could be samurai has been turned on its head with the discovery of two letters written by feudal warlord Toyotomi Hideyoshi to acknowledge a woman as head of a samurai clan.

The historical documents were found in the home of a long-established family here.

Hideyoshi (1537-1598) sent the letters to Munakata Saikaku of the Munakata clan, famed for producing successive generations of “daiguji,” the highest-ranking priest of Munakata Taisha shrine.

Saikaku is believed to have been married to Ujisada, the last daiguji of the Shinto shrine, which is a part of a UNESCO World Heritage site.

The discovery of the letters, announced by the town’s board of education on Sept. 18, immediately attracted a flurry of attention nationwide.

The two rare letters, one a “hanmotsu” official document signed with Hideyoshi’s “kao” stylized signature, and a “shuinjo” letter with a red seal, were handed down through successive generations of the Munakata clan, which served the ruling Hosokawa clan of the Higo Domain, present-day Kumamoto Prefecture.

A descendant of the Munakata family who lives in the town approached local officials with an offer to donate the letters.

Okifumi Hanaoka, an academic researcher at Kyushu University’s Faculty of Social and Cultural Studies, and other experts studied the documents for authenticity.

Ujisada died suddenly in 1586, the year before Hideyoshi conquered the Kyushu region. Hideyoshi praises the Munakata clan for stopping the Shimazu clan, which was based in southern Kyushu, from heading north. In gratitude, he issued the hanmotsu that same year guaranteeing that the clan can retain its territories.

In the shuinjo, the warlord instructs the Munakata clan to consult with his vassal, Asano Nagamasa, before sending troops to Kyoto.

Both letters were addressed to Saikaku, showing that Hideyoshi acknowledged Ujisada’s wife as head of the Munakata clan.

Although Saikaku is mentioned as the lord of the Munakata clan in letters passed down to other samurai families, little had been known about her.

“It became clear that Saikaku led the Munakata clan after Ujisada’s death and passed down its name,” Hanaoka said.