This battle is a breeze if you gained ronso trust...and a songstress will die very quickly without sufficient priotection and healing. So, equip one white mage with at least Dispel, Cura and Protect learnt and cast on all three characters at once (by pushing down the right d-pad button). Have one Warrior to use powerbreak and such alike and a powerful dressphere to deplete the hp quickly, he does attack very fast so i suggest equipping Highroad Wings garment grid so you can start immediately