Miburo ni Tsubasa

In late-Edo Kyoto, a young tengu girl named Shion sets out alone to pursue her older brother, who slaughtered their clan and stole all of their hearts. When she is attacked by a samurai who has turned into a monster after eating a tengu's heart, she is saved by Heisuke Toudou, a member of the Mibu Roushigumi who would later become the captain of the Shinsengumi's eighth unit. In order to stop her brother's ambitions and avenge her fallen kin, Shion begins living in the human world with Heisuke and his comrades.

(Source: Hakusensha, translated)