Stage Fifteen: Abyss Bridge
Enemies: Snuff Imp lvl 6 x3
Manikin lvl 7 x3
Witch lvl 8 x1
The only bridge across the gorge between you and Aerei is guarded by a Witch and her summoned imps. Although not as powerful as Malevolenta, the Witch will still throw Fire spells at you from the safety of other side of the bridge, and her bevy of attendant imps will join in with Fireballs.
This is not a battle where you can hang back and let the enemies come to you, as they will refuse to do so. Your only choice is to storm them, and the only way to do this is by crossing the bridge (or by fielding a group entirely comprised of Crows to fly over the chasm, but this is rather impractical). Of course, crossing the bridge is going to be a slow process, and you're going to be pelted by flames the entire time. This sounds like a job for a magic-defense tank, like, say, oh...Søren?
With Søren to lead your advance, deploy some similar tanky types with high magic defense (Familiars, Elementals) or, failing that, high HP (Flo, Manticores). Since the enemies are trapped in tight quarters on their side of the bridge, area spells from Elementals or Yuki can put a large dent in their collective strength, allowing your advancing tanks to wade in and finish them off.