Flame in the Mist by Renée Ahdieh

The only daughter of a prominent samurai, Mariko has always known she’d been raised for one purpose and one purpose only: to marry. Never mind her cunning, which rivals that of her twin brother, Kenshin, or her skills as an accomplished alchemist. Since Mariko was not born a boy, her fate was sealed the moment she drew her first breath.

So, at just seventeen years old, Mariko is sent to the imperial palace to meet her betrothed, a man she did not choose, for the very first time. But the journey is cut short when Mariko’s convoy is viciously attacked by the Black Clan, a dangerous group of bandits who’ve been hired to kill Mariko before she reaches the palace.

The lone survivor, Mariko narrowly escapes to the woods, where she plots her revenge. Dressed as a peasant boy, she sets out to infiltrate the Black Clan and hunt down those responsible for the target on her back. Once she’s within their ranks, though, Mariko finds for the first time she’s appreciated for her intellect and abilities. She even finds herself falling in love—a love that will force her to question everything she’s ever known about her family, her purpose, and her deepest desires.