On the night of September 18, 1863, Serizawa Kamo, co-commander of the early Shinsengumi, was assassinated at the Yagi residence in Mibu, Kyoto. A powerful warrior from the Mito domain, Serizawa had co-led the organization alongside Kondo Isami, but his violent behavior and drunken rampages had caused repeated problems. That night, after drinking heavily, he was ambushed in bed by assassins including Kondo and Hijikata. His mistress Koume and fellow corps member Hirayama Goro were also killed. The assassination is said to have been carried out with the tacit approval of the Aizu domain. After Serizawa's death, Kondo Isami took sole command and, in the dual-leadership system with Hijikata Toshizo, drove the modernization and disciplinary tightening of the corps. The event is inscribed in Bakumatsu history as emblematic of the Shinsengumi's internal power struggles.