This guy was a loser but people did not let him know that he was one. They hid that fact from him and this mistress felt that they were not doing him any justice. So she chose to tell him and she also humiliated him for good measure. He was humiliated but the mistress did not care as it was time for him to know and then deal with it.
Goddess Kira wanted to find a way to control this guy and she did it with her chastity key. It was a lot of fun for her and she had a great time doing it. The mistress wanted something which was easy for her and she found it in the chastity key. She had him wear a chastity device and when she was done having him wear it, she hid the chastity key and controlled him.