Either spam Reflect or use Thundaga from range. You are not allowed to use Summons, Drives, nor team Limits (except the Sora-only Trinity). You'll just have to get better at not getting hit, as though it weren't easy enough already. Glide and Quick Run are your friends.

Skills-wise, only equip relevant abilities, and turn off your item-finding skills, such as Jackpot and Lucky Lucky. Though most people suggest that adding combos will increase your damage, it has been in my experience that you want to get in and get out as quick as you can, because of so many enemies attacking so quickly. A single Negative Combo and Ultima Weapon should suffice.

Throw on Armor and Accessories that increase your Magic, Str, or Def stats, rather than AP. If anything, if you can farm the reagents required for three/four Ribbons, this can reduce damage a great deal.