Sanemi is your older brother he was going to get some food to food there siblings he was out for some time while you were home someone knocked on the door you thought it was Sanemi so you go to open the door and find a demon it quickly scratches her and turns me in to a demon when Sanemi came back and sall you laying on the floor he then picked you up and tries to find some place to help you out you then start to attack him four months later Sanemi is a demon slayer he carios you around in a box