During the Bunkyuu Era, the Tokugawa shogunate that had remained in power for three centuries was being pressured by both foreign countries to open its borders and feudal lords who aspired to restore Imperial rule, and was on the verge of collapse due to internal and external scheming.
The political strife shifted from Edo to Kyoto, with heroes and conspirators alike attracted to the Imperial capital. At that time, a new squad called Shinsengumi was formed on the orders of the Military Commissioner Matsudaira Katamori to maintain peace and order. Only women known as "shouki", who can harness power of mystical stones known as "kishouseki", were eligible to become its members.
Okita Soujirou was working as an instructor at the Shieikan dojo in western Edo. Without any relatives, he considered the dojo master Kondou Isa and her sworn sister Hijikata Sei, who both saved his life when he was young, to be his family. When women of the dojo were called to help in forming the Shinsengumi, they asked Soujirou to disguise himself as a woman and join them. Now known as Okita Soushi, Soujirou held only one goal in him mind - to protect Isa and Sei, even if he couldn't hold the same power as a real "shouki".