Special Ability Preliminary Voting

This is going to sound rather...cheap...but I vote for:

Aether and Summon

but not in the traditional sense. I think both could be implemented simultaneously.
I prefer to think of the Aether ability as Iris consuming the spiritual essence of powerful entities, granting her their powers, but not being able to control them. I like Summon because it hearkens to her unstable and immoral infusion of espers, and in the same sense, she is really actually consuming the esper itself being able to force its pure essence out as much as she likes and cast all of its powers.

With the "Magic" command you might be able to pull off the 'Esper Magic' and give her constant access to the 'summoning' in the magic window. This will give her Magic, but unlike the others, she won't have access to each and every spell, which is why Aether would boost her playability by giving her very powerful (however uncontrollable) abilities that no other character has access to.