Shinakoi manga

Shinakoi summary:

Sakura is an incredible kendo fighter who uses an abnormally short shinai. She regularly trounces boys who underestimate her skills. One day two kendo fighters, even stronger than her sensei, attack her dojo asking questions about someone called Narukami Koharu. Apparently, there is a lot Sakura doesn't know about her family history, and it could very well get her killed. Now, Sakura must try to live up to her father's legacy.