"Hitokiri" Shoujo, Koushaku Reijou no Goei ni Naru

Shurine is a girl who has mastered the sword, raised to serve as a bodyguard. However, when she is falsely accused of an assassination attempt, she is forced to go on the lam. Driven into exile, Shurine meets Lutecia, a duke's daughter whose life is in danger, embroiled in a dispute over succession. When Lutecia is attacked by an assassin, Shurine makes her an offer.

(Source: Micro Magazine-sha, translated)