Heals, heals, and more heals.
Empowered abilities and resource manipulation
Your attacks and abilities send Aery to a target, damaging or shielding allies.
Periodically your next ability used has its mana or energy cost refunded and restores some of your missing mana or energy.
Gain 3% extra MS. Gain extra AP or AD, based on your bonus MS, Adaptive.
Your first ability hit every 20s burns champions.
+65 health and +10 AP or +6 AD, adaptive
Heals and shields are 5% stronger and increased by an additional 10% on targets below 40% health.
Impairing the movement of an enemy champion marks them. Your allies heal when attacking champion's you've marked.
Summon Aery is a great option for Soraka both offensively (with autos and [Q]) and defensively (with [W]).
Manaflow Band is a great option here for Soraka because you're going to want to play aggressively in lane early spamming [Q].
Celerity on Soraka allows you to position yourself safely in teamfights and skirmishes so that you're able to continue pumping out heals.
As a added benefit, when your passive kicks in and you get the Bonus Movement Speed towards low allies, Celerity will grant a bit more extra AP to empower those heals.
Scorch allows you to dominate the lane phase if you're able to consistently land your [Q].
Because you're going to be healing so much over the course of the game, Revitalize gets fantastic value, especially if the target is low health.
Font of Life doesn't seem like an obvious choice but if you can land your [Q] regularly it synergies well with your itemization and Revitalize.