Manga Musical "touken Ranbu" Bakumatsu Tenrouden

It is the year 2205. The “Historical Revisionists” have begun attacking the past. In order to prevent history from being altered, the Time Government has sent “Saniwa” to the past. Awakened by these Saniwa are the tsukumogami dwelling in swords, “Touken Danshi”. In order to protect history, they throw themselves into battle. The Saniwa gives their Touken Danshi the order to go on a new sortie. They assign a formation with Hachisuka Kotetsu as the captain, Kashuu Kiyomitsu, Yamatonokami Yasusada, Izuminokami Kanesada, Horikawa Kunihiro and Nagasone Kotetsu. Hachisuka Kotetsu is rubbed the wrong way by the existence of Nagasone Kotetsu, who is a forgery.
The stage is the first year of the Genji era (1864). The target of the Historical Revisionists is the Shinsengumi. Kashuu Kiyomitsu and Yamatonokami Yasusada were Okita Souji's swords, Izuminokami Kanesada and Horikawa Kunihiro were Hijikata Toshizo's swords, and Nagasone Kotetsu was Kondo Isami's sword. Seeing their former masters makes the Touken Danshi waver. However, the presence of the History Retrograde army, under the command of the Historical Revisionists, draws near them. What is the meaning of Yamatonokami Yasusada's actions, as the goal of the History Retrograde Army remains unknown...?