Nagakura and Harada, taking with them some other members, joined with a group of former Tokugawa retainers with Haga Gidou being one of them to form a new unit, the Seiheitai. Nagakura and the Seiheitai unit left Edo shortly after Edo Castle's surrender, and participated in some battles in the Battle of Utsunomiya Castle and at Imaichi and headed north, hoped to take part in the fighting that was moving northward, toward Aizu. But upon receiving news of the surrender of the Aizu Domain, Nagakura returned to Edo. While in Edo, he had to hide for a while because he had fought against the Imperial forces and would turned himself in to the senior councilor Shimokuni Toshichiro of the Matsumae clan and served as an infantry instructor and was stipended at his father's original rate of 150 koku. However, he would often run into Suzuki Mikisaburō, the younger brother of deceased Itō Kashitarō and one of the four Shinsengumi defectors who narrowly escaped from the assassination attempt during the Aburanokōji incident back then in December 1867. Due to his involvement in that incident and suspecting that Suzuki was trying to kill him, Nagakura returned to Matsumae, Hokkaido in late 1868 (Meiji 1). In 1871 (Meiji 4), Nagakura married , daughter of the physician (). In 1873 (Meiji 6), he was adopted into his wife's family and changed his name first from , and later . Their only son, was born on February 24, 1873. Later in 1875, Sugimura Yoshie, with the help of the physician Matsumoto Ryōjun and several surviving former Shinsengumi comrades including Saitō Hajime (as Fujita Gorō) among others, erected the monument known as the "Grave of Shinsengumi" for Kondō Isami, Hijikata Toshizō, and the fallen comrades of the Shinsengumi at Jutoku-ji temple boundary in Itabashi, Tokyo and held requiems for their past comrades' souls. In 1882 (Meiji 15), Sugimura moved his family to Otaru, Hokkaido, and was invited by the police bureaucrat Tsukigata Kiyoshi to work as kenjutsu teacher to train the prison guards in Kabato prison for four years.