After the defeat of the Ryūzōji clan at the Battle of Okitanawate in 1584, Shimazu Yoshihisa refocused his attentions on the Ōtomo clan and a campaign was started against their dominions.

The siege of Iwaya Castle resulted after the Shimazu invasion of Chikuzen Province.

The castellan of Iwaya was Takahashi Shigetane, one of the most trusted retainers of the Ōtomo, and held the fortress with a small garrison of around 763 soldiers.

[1] When Shigetane realized he could not hold the fortress any longer, he committed seppuku and all soldiers suicide attack.

The Shimazu took the castle and were impressed with Shigetane's loyal conduct; they are said to have prayed for his deceased spirit.