Yukariko.

The time is the Azuchi-Momoyama Period. While Yukariko is a woman, she is by nature masculine and, as she was raised in a family with no heir, she learned general martial arts. Then an unexpected story is told to Yukariko, whose father died suddenly. It is said that because Yukariko is the daughter of the daimyo of Aki, and twins with the current feudal lord, she was given to an adoptive family in secret. As a matter of fact her brother the feudal lord, Midorio, is ill, and in order that the other provinces may not know, she is told that he wants her to serve as his substitute....