One day I picked up a young lady who had fallen into the water. She was very obedient and knew all my hobbies and would take every important day of my life seriously. I fell in love with her undeniably until I confessed to him and she suddenly disappeared from my life as if she had never appeared. No one except me remembered her.
Note that the protagonist is a real mother and daughter. "I" really fell in love with her daughter but she didn't know that she was her daughter. The daughter also loved her mother, but it was just a mother-daughter relationship. In the end, the daughter killed the scumbag and disappeared in order to save her mother from being killed by the scumbag. The mother also found out the truth and met her husband after doing so.
Purpose: Save Time Travel