Crimson Empire [JP]

Crimson Empire - Circumstances to Serve a Noble: The heroine is a head maid who has sworn absolute loyalty to Edvard, a prince, and would do anything to assist him to the throne.

There are 2 princes who are fighting for the throne, Edvard and Justin. But because Justin's mother was of a lower rank, Edvard has more of a right to the throne. Therefore, Justin plots to assassin Edvard to get to the throne. The problem though, is that every time he sends an assassin, the heroine would defeat the assassins.