On the 21st (although rumored to have in fact been on 22nd), Saigo made a secret agreement with the Saccho Teikei Rokkajo (six articles of partnership between Satsuma and Choshu) with Kogoro KATSURA at Tatewaki KOMATSU's residence, and Ryoma SAKAMOTO endorsed a corporate document (Satsuma-Choshu Alliance).
21日（22日という説もある）、西郷は小松帯刀邸で桂小五郎と薩長提携六ヶ条を密約し、坂本龍馬がその提携書に裏書きをした（薩長同盟）。