Harunobu was the daimyô of the Arima clan, a small family that controlled the Shimabara area of Hizen province. Arima Yoshisada's son and successor, Harunobu began a persecution of the Christians in his domain after his father's death. In 1579, with Ryûzôji Takanobu expanding into the area, Harunobu - like his uncle Ômura Sumitada - turned to the Jesuits for assistance. In return, he was baptized as Protasio and ended the persecution, even going so far as to order the destruction of all (Buddhist) idols and the conversion of all people in the territory; by 1582, some 20,000 residents of Arima lands had been baptized. The arrival of Portuguese weapons and ships bought the Arima a little time, but in 1582 Harunobu lost his important Shimabara Castle and was reduced to holding a thin strip of the peninsula. In desperation, he turned to the Shimazu clan, presently at war with the Ryûzôji in Higo province. The Shimazu dispatched a force under Shimazu Iehisa to Shimabara and in 1584 they and the Arima, with a combined 3,000 men, defeated the much larger Ryûzôji army at Okitanawate, a battle in which Takanobu was killed. Afterwards Shimazu Yoshihisa suggested the Arima renounce Christianity but did not press the issue when Harunobu declined.
Arima attached himself to Toyotomi Hideyoshi after the latter invaded Kyushu (1587) and in 1593 led some 2,000 men to Korea under Konishi Yukinaga. Harunobu supported the Western side in the Sekigahara Campaign (1600) but did not suffer the loss of any land as a result.
In 1609 Harunobu was sent on an expedition to Formosa (Taiwan) with the intention of scouting out a potential trade center for Japanese, Chinese, and Western ships. When they arrived, the island's inhabitants set upon Arima's men and a fair number of them were killed. (The next attempt to conquer this island, in 1616 and evidently led by the Ômura, also ended in failure).
Harunobu was also involved in the sinking of the Portuguese ship Madre de Dios in 1609 and was rewarded for his efforts; in 1612, however, he fell out with Tokugawa Ieyasu and was executed on the grounds of treason.
- Initial text from Sengoku Biographical Dictionary (Samurai-Archives.com) FWSeal & CEWest, 2005
- William Theodore de Bary, Carol Gluck, and Arthur Tiedemann (eds.), Sources of Japanese Tradition, Second Edition, vol 2, Columbia University Press (2005), 148.