Demon Chimera starts the fight by inflicting all elemental resistance down on your team. It has a counter ability that can reduce accuracy and an attack that can reduce AGI. Aside from that, Demon Chimera doesn't actually hit that hard to need high defenses.
After a few turns, 4 Bandits will show up as reinforcements. 2 Samurais on the sides near the center of the map, while the 2 Gunners are near your team's initial spawn location. If you have strong Light mages then they can be easily one-shottable. They don't really deal that much damage either, but after the debuffs from Demon Chimera, it can be an issue if your team's not that prepared.
All enemies are Dark elements and weak to magic type. Sakura can pretty efficiently handle Demon Chimera and the bandits, but other Light units are pretty usable too.
Ildyra can heal and also has Holy. Her limit burst increases CT so it can help with bursting down the enemies.
Carbuncle esper has magic attack+, and demon and dark killers, so it can be used on any of your damage dealers to get some easy boost.