Whether or not she cheated Ieyasu into joining the Takeda clan; the veracity of this event remains one of the greatest mysteries of the Sengoku period, known as the Nobuyasu Incident.

[2] Knowing his eldest son would feel obligated to avenge his late mother's death, Ieyasu eventually ordered Nobuyasu, who was confined at Futamata Castle (now Tenryū Ward, Hamamatsu), to commit suicide (seppuku) on 5 October 1579.

On the other hand, Kuroda also stated that the story about Nobunaga as the one who ordered the execution solely based on Mikawa Monogatari (三河物語), an early Edo period source with a heavy Tokugawa slant.

Such faction was spearheaded by Tsukiyama and her son Nobuyasu, which Ieyasu viewed as problematic as they have implied their collaboration with the Takeda even before the Battle of Nagashino.

[3] Other evidence supporting this theory is that Tsukiyama may have started the pro-Takeda faction as a means of revenge, since Nobunaga was responsible for the death of her uncle, Imagawa Yoshimoto.

[3] Other historians and Sengoku period experts such as Watanabe Daimon,[4] Taniguchi Katsuhiro, Honda Takanari, Hirayama Masaru and Shiba Hiroyuki also opined that her execution was Ieyasu's personal initiative.

[3] Only Kazuto Hongō among modern historian who still supported the classical theory which stated Nobunaga as the one who ordered Tsukiyama's execution.