Bishôjo kenshi: Tsuki ni mukatte o shigoki yo!

Overview:

While working part-time at an izakaya, Yuko practices sword fighting at a dojo with her boyfriend Kenji. One day, Hiromi, who claims to be her long-lost sister from 19 years ago, appears before her. Yuko is surprised, but believes Hiromi when she tells her a secret that only her family knows, and they begin living together...