Tsukiyama-dono, Ieyasu's principal wife, was suspected of colluding with the Takeda clan and put to death — a suspicion traditionally said to have originated with his ally Oda Nobunaga. Wary of her Imagawa lineage, Nobunaga reportedly pressed Ieyasu to act, leading to the 1579 Tsukiyama-dono Incident, whose memorial tower still stands at Sairaiin.