I'm looking for an old story that I really liked.
The good girl meets a friend and tells him that she challenged the bad girl. He is worried and follows her.
He goes to watch the match but immediately realizes that the bad girl is physically stronger and he fears for the good girl.
However, he cannot intervene because he is immobilized and he has to witness the massacre.
The bad girl destroys the good girl and sometime she goes to sexually stimulate the boy, who cannot resist.