In 1582, Oda Nobunaga's invasion of Kai Province drove the Takeda clan to the brink of collapse, and Takeda Katsuyori sought refuge at the seemingly impregnable Iwadono Castle. Castellan Oyamada Nobushige betrayed him and refused entry, forcing Katsuyori to take his own life at Mt. Tenmoku. The castle thus became the stage for one of the late Sengoku period's most famous tragedies, set in motion by Nobunaga's campaign.

In March 1582, as the Oda-Tokugawa invasion of Kai crushed the Takeda, Takeda Katsuyori sought refuge at Iwadono Castle held by his retainer Oyamada Nobushige, only to be refused entry and abandoned. With nowhere left to go, Katsuyori fled to Mt. Tenmoku, where he and his family took their own lives on March 11 — a betrayal remembered as one of the most famous episodes marking the fall of the Takeda clan.