In 1575, Katsuyori lost the Battle of Nagashino, a disaster for the Takeda clan which left Nobutomo at Iwamura Castle without support. Under repeated siege by Oda Nobutada, the forces under Nobutomo managed to hold the castle until November when Nobunaga swept in with the main army. Nobutomo signed a truce to surrender the castle after realizing that he had no chance to hold out any longer. Unfortunately, Nobunaga broke the truce and ordered Nobutomo, his wife (Nobunaga's aunt), and the troops of the castle garrison to be executed.
On December 28, 1575, Nobutomo and his wife, the Lady Otsuya, were crucified upside down along with his elder retainers Oshima Nagatoshi and Zakouji Sadafusa on the banks of the Nagara River.