Ciel

Ciel was a high-ranking Idol Magus working for the organization Ideal. Originally appearing as a cheerful singer, Ciel is later revealed to be a spy working for Ideals leader, Weishiet and had her memories wiped many times by him. Ciel was originally supposed to monitor you and eventually kill you but after being treated kindly and falling for you, Ciel would abandoned her original mission and was willing to sacrifice herself for you. However, you managed to save her and promised to protect her, which made her wanting to stay with you.