Leave the Fake and come back later for it. You won't get much of a reward anyway so don't even bother with it really. You can only hurt those with magic and your party isn't magically strong enough yet (least I don't think).
Did you get familiar with turning on and off AI controller party members' techs yet? If you did and Genis has spells that'll do Efreet more harm use only those

I'm not talking about forgetting a tech, you can actually turn their useage on and off. RTFM.