In March 1869, after hearing reports of incoming Japanese forces plans to captured Hokkaido, Gengo leads a group of sailors (including Arai Ikunosuke and Hijikata Toshizō) and French Army advisors (including Jules Brunet, Arthur Fortant, François Bouffier, Jean Marlin, and Pierre Garde). Gengo seems to have been the center of the operation because of the belief that "Let's attack aggressively rather than waiting for the enemy". The flagship "Kaiten Maru", commanded by Captain Gengo, arrived at Miyako Bay along with the "Banryu Maru" and "Kaohsiung Maru", but due to bad weather, the "Banryu Maru" strayed and the "Kaohsiung Maru" broke down. Only "Kaiten Maru" will enter the Battle of Miyako Bay. It had said that Gengo said in his final word before the attack, "Even my ship is enough to defeat the enemy." 