Angelique Maren no Rokukishi

Teresa has been living a normal life with Renaud, who is like a younger brother to her, until odd disappearances start happening across town. First Teresa was abducted, and although she returned home unharmed, she remembered nothing about the incident. Her family decided to put it behind them, but soon Renaud disappears, and unlike in Teresa's case, he has been gone for days.

While searching for her brother, Teresa reached a fortress. There, Renaud was entertaining some sort of notion that he has become the leader of a group of knights. Determined to take her brother home, Teresa poses as one in the team to find out what happened.

[Edited from Play-Asia]