Yep, definitely a ghost... Eren watches another lightbulb go out and has to suppress the urge to bark out an angry remark - accidents happen, right? And the more Clara's words come into focus for him, the more sympathy he begins to feel.

“From Redbright?” he repeats, giving Heiji a suspicious look. (They’d have to save the 'so you can see supernatural stuff, huh?' conversation for later, when they aren’t dealing with a distressed ghost.) He’d gone to Redbright for a short time. While his stay had ended rather drastically, he’d been there long enough to make a few acquaintances – one of which, oddly enough, he’d seen somewhat recently... “Hey, if you're talking about one of the students there, they wouldn't happen to be a short girl, would they?”