Youko Sumeragi

A woman who appears in a book-world that corresponds to the Russo-Japan War era. She is an intelligence agent and an expert martial artist noted for sending three colleagues into hospital during training. Yōko arrives on a train somewhere corresponding to contemporary Russian Siberia, cross-dressing as a male diplomat and attempting to link up with fellow agent Kohtaro Nanbu, codenamed "Adam", for a film containing radio codes. Due to her inexperience, however, she quickly becomes the subject of suspicion and is only rescued by Kazuo Saiga, another fellow agent known as "Tiger of Siberia".

Although Kazuo turns out to be a double-agent whose henchmen end up killing Kohtaro, Yōko is able to defeat him and complete her mission with Hazuki's help. (Wikipedia)