Later, in the Koyo Chinbutai (a military unit formed specially for the campaign in Kai Province) he distinguished himself as the chief of the direct attendant group on Commander, and when Isami KONDO surrendered to the New government army in Nagareyama and presented himself at the government-general in Itabashi, Soma visited Itabashi to beg for Kondo's life with the letter of Shogunate Army Gunjikata (officer in charge of military affaires), Gennojo MATSUNAMI.
その後、甲陽鎮撫隊では局長付組頭として頭角を現し、流山で近藤勇が新政府軍に投降し、板橋の総督府に出頭すると、幕府陸軍軍事方、松濤権之丞の書状を携え、近藤の助命のために板橋を訪れた。