On the 17th day of the 11th month (shimotsuki) of 1285, Adachi Yasumori — the most prominent leader of the shogunate's vassals — was destroyed by Taira no Yoritsuna, the steward (uchi-kanrei) of the young regent Hōjō Sadatoki. Yasumori, father-in-law of the late Hōjō Tokimune, had led reform efforts known as the "Kōan Tokusei" and handled rewards for the defenders who had fought the Mongol invasions. After Tokimune's death in 1284, Yasumori clashed with Yoritsuna, who had risen as the confidant of the nine-year-old Sadatoki. Yoritsuna whispered to Sadatoki that Yasumori plotted to become shogun and launched a surprise attack on Yasumori's mansion at Matsuyagatsu in Kamakura. Yasumori, his son Munekage, and more than 500 kin and retainers were slain, and Yasumori's faction was purged across the country, with casualties said to reach thousands. The incident crippled the power of the gokenin houses and established the autocracy of the Tokusō (Hōjō main line) and its inner stewards — a fundamental reshaping of Kamakura governance.