Yeah, I had trouble with this guy for a while, too. I ended up waiting and relevling my people up to 13-14 on average. Plus I made sure I had at least two people with Quickenings in my starting fighting party... three if you want a very quick win.

Tip 1 is to not bother trying to take down the other judges, at all. Focus on Judge Ghis. If you've got 3 people with Quickenings, put two in your starting party and the third on reserve.

Right off the bat, hit him with a Quickening and, if at all possible, link them. Basically if you see one of your PS2 button symbols appear beside a name, press it. If nothing shows up, keep hitting R2 until one does show up, THEN press it.

Hopefully you'll get at least 2 quickenings linked. After the quickening is done, hammer Ghis with a few attacks/spells. Then switch out one of your party members for that third person with a quickening available... and use it on Ghis again.

If he isn't down by then, he'll be very, very, very close. Good luck!