He is pain to hit when at airborne, but every once a while he slams onto ground for few seconds, that's when his weak point is exposed and you'll do plenty of more damage. Try to use fire-based attacks on it for extra damage.
Barachiel is the 2nd boss. Do you mean Sahariel? He's the third. I'll assume you mean Barachiel.
He will take you quite a few minutes, so be ready to sit down for a long battle.
I used Reimi to kite it, running away and hitting when I could, while generally keeping out of range of its AoE explosions. If you gave her the taunt skill that helps. Heal with Lymle if she's learned the spell.
When it pounds the ground its weak spot appears in its back. Hit it hard and it will resume flying. Some moves, like Reimi's first skill, will pierce through the boss and hit the orb even if she's in front of it. If you have the torch bow use that, as it's weak to fire (Lymle's spells also apply if you want to use Cerberos).
There are actually a lot of threads about this boss on the forum if you want to perform a search.
Bane even prayed for Dick when he became Batman. -- Frostbite_Zero
dude its not the boss that is driving me crazy.. its the AI of the other character.. is there like tactic like in SO3 that a character can focus on healing? It's really annoying that I am at 50% and get kill while trying to heal myself with casting animation
Use Reime the fight becomes so freakishly easy. Her blindside allows her to avoid his ground smash attack 90% of the time plus he is weak to fire and she should have the torch bow. Once you use blindside her bow will do great damage. Reime is the key to this battle. Hope you know how to use her.