Aerith is more or less a support-oriented unit that's best described as an "affinity" unit. Her counter ability and Protective Familiar are decent abilities that will make you want her to stay close to your main units, which will also end up giving affinity bonuses. Since she can increase her SPR and area attack resistance, as well as the team magic barrier, she's more suited to bring against magic damage dealers.
As a support-healer, she only has 1 heal ability (2 if you count LB) and her only form of revival skill is Reraise, which unfortunately is unlocked at job level 25. But as a general support, she does have some useful CT related skills and the incredibly useful Quicken from Time Mage sub job. She can potentially be built more towards a magic damage dealer through Rune Knight sub job, but most of her attack abilities have awkward range.
Similar to Barret, her role in the party might be somewhat niche. She won't exactly be a "main" support that fills all the things that you might want, but she can be useful in certain setups that needs what she can offer.
Restores HP (L) of allies within range & raises DEF for 3 turns.
Effect Type
Magic
AP
58
UseLimit
1
Max Effect (at Lv.20)
Hp: +310x, DEF: +15
Range Height
2
Area Height
1
Master Ability
Master Ability 1
Water Unit Allies' Max HP +10% / Water Attack +15, own MAG +15% / SPR +5
Master Ability 2
Own SPR +20 / Slash/Magic Attack Res +20% / Non-Attack Skill Activation Time -200
Dream Ability
Own HP +15% / Area Attack Res +15 / Reraise (White Mage (FFVIIR)) Skill Upgrade: Bestows Reraise on target, allows unit to automatically recover from KO status once per battle (HP recovery (Min)) & raises CT (S) after revived by Reraise Effect.
Bestows Reraise on target, allows unit to automatically recover from KO status once per battle (HP recovery (Min)) & raises CT (S) after revived by Reraise Effect.