The Story of Zoe
Zoe was a girl from Targon's foothills who was chosen by the Aspect of Twilight — the cosmic entity that embodies chaos, disruption, and the space between things — to be its mortal host. This happened several thousand years ago. In the time since, she has watched every mortal friend she ever had grow old and die while she remained exactly as she was when the Aspect chose her: a teenager, eternally, with the attention span of someone who processes time very differently from everyone around her.
The Aspect of Twilight is not a dignified or structured power. It is the cosmic force of magic's chaotic potential, the thing that doesn't fit categories, the energy of change for its own sake. It chose Zoe specifically, by all indications, because her chaotic nature was a better vessel than someone stable would have been. This is either a profound statement about the nature of cosmic power or a decision that has caused several thousand years of collateral damage. Both may be true.
She appears in places where cosmic significance is happening — around mortals the Aspects are watching, around events that will shift the balance of things — and she meddles in ways that are neither helpful nor harmful in any predictable sense, because "predictable" is not a concept the Aspect of Twilight embraces. Ezreal finds her interesting and slightly alarming. This is the correct response. She has been watching him for longer than he knows, which he also hasn't asked about, which is probably for the best.