Tsunade's hemophobia was, at its core, caused by psychological trauma stemming from the deaths of her younger brother and her lover.
Especially her lover, Kato Dan: by the time Tsunade arrived, he had not yet breathed his last, but he died in her arms covered in blood. Watching her lover bleed to death in her arms while her proudest medical ninjutsu failed to save his life left her with symptoms of trembling all over and mental collapse at the mere sight of blood.
As the saying goes, a sickness of the heart requires a remedy of the heart. Li Fusheng's treatment plan was to cast an illusion on Tsunade, and then have someone she cared about severely injured in front of her, thereby arousing Tsunade's courage to save her loved one and conquer her hemophobia.
Chapter 156