Sanshirou²

From the Animeraider:

Sugata Sanshirou has been studying martial arts in the wilderness, becoming strong and fast. When Sanshirou’s grandfather tells of a promise made long ago to a family friend he tells Sanshirou it is time to go to the city and meet the girl Sanshirou is engaged to. It’s a shock, but Sanshirou goes to the city.
Toyotomi Sanshirou is a young man with some fighting experience in the city, and some training thanks to his grandfather’s doujo, but he’s not really into it – although he won’t back down from a fight or from defending his family’s honor. He comes home one day to find his sister Mifumi arguing with his grandfather about an arranged marraige to a boy with the same name as him. He believes this is his way out of being the top fighter in the doujo and he welcomes the pending arrival of this new Sanshirou as his ticket out of there.

Okay, two problems (and you knew that they would be there). One, Sugata Sanshirou is a girl, and two, she’s determined and honor bound to become the wife of the only son at the Doujou – namely, Toyotomi Sanshirou.

Oh, and one more thing – she’s stronger than everyone else at the Doujou combined. Perhaps stronger than everyone in the city combined…