Kai Doh Maru

Kai Doh Maru is the story of Kintoki, a girl, who was disguised as a boy at an early age to protect her against the enemies of her house. While disguised as a boy Kintoki's cousin, Princess Ouni falls in love with her, not realizing that Kintoki is actually a girl. Kintoki fled from her cousin's love and becomes hunted by her scheming uncle - until she is rescued by a noble samurai warrior, Lord Raiko. Kintoki spends the next few years under Lord Raiko's protection, learning how to use a sword. Kintoki eventually joins with Lord Raiko and his subordinates and becomes a warrior entrusted with protecting the city from bandits.

Synopsis from Anime News Network