I played up to that part yesterday, still around that part too. Riddle talked about the prisoned all man. How Lynx killed Viper, how some guy betrayed Viper. Something about Zoraban or something being related to Riddle. Something like how the Frozen Flame is a fire frozen in time and it was passed down from hand to hand till it got to General Viper, whom gave it to Riddle. Well, since the FF touched Riddle last, maybe that's why she is an arbiter? Like how Serge became the arbiter because he came into contact with it too.