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]

The protagonist is an orphan who has no memories of her parents. She is raised by a family acquaintance and acts as the elder sister for their son, Renaud. One day, Renaud is missing and the villagers fear the ensuing wars too much to look for him. When the protagonist searches for him, she learns he has been recruited by Leviath and is one of his knights. The protagonist fears for his safety and decides to stay with the knights. As she does, she learns that she harnesses a mysterious power which helps Leviath's cause and learns about her lost past.