Iwamura Castle was defended by Otsuya no Kata, aunt of Oda Nobunaga, as its female castellan. During the Sengoku period, Takeda Shingen's army and the Oda clan fought fierce battles for control of the castle. As one of Japan's three great mountain castles, its history shows how Shingen's power once extended into eastern Mino.

Lady Otsuya, Nobunaga's aunt and castle regent, defected to the Takeda in 1572. Nobunaga retook the castle in 1575 and executed both Lady Otsuya and the Takeda commander Akiyama Torafusa. He then installed loyal retainers as castellans, making Iwamura a key stronghold for consolidating his control over eastern Mino.