Series title and numeration from NoveList.

The daughter of a prominent samurai, Mariko has long known her place--she may be an accomplished alchemist, whose cunning rivals that of her brother Kenshin, but because she is not a boy, her future has always been out of her hands. At just seventeen years old, Mariko is promised to Minamoto Raiden, the son of the emperor's favorite consort--a political marriage that will elevate her family's standing. But en route to the imperial city of Inako, Mariko narrowly escapes a bloody ambush by a dangerous gang of bandits known as the Black Clan, who she learns has been hired to kill her before she reaches the palace. Dressed as a peasant boy, Mariko sets out to infiltrate the ranks of the Black Clan, determined to track down the person responsible for the target on her back. But she's quickly captured and taken to the Black Clan's secret hideout, where she meets their leader, the rebel ronin Takeda Ranmaru, and his second-in-command, his best friend Okami. Still believing her to be a boy, Ranmaru and Okami eventually warm to Mariko, impressed by her intellect and ingenuity. As Mariko gets closer to the Black Clan, she uncovers a dark history of secrets, of betrayal and murder, which will force her to question everything she's ever known.

HL720L Lexile.