@karasutengu A new chew toy?
I've been figuring Eri would be instigating Sumire (and Eugene). While Sumire does seem to have a crush on Eugene, I don't really see her as someone who'd take the first step, at least not intentionally, on her own.
For example, in this chapter while Sumire did glomp Eugene, she very quickly realized what she did and backed off. I'd interpret the glomping as part of her new Ifrit race making the first move (i.e., a fiery personality) and backing off as her natural personality caught up realized what happened and took over.
Eri strikes me as someone who's incredibly bored and skilled with people. Instigating Sumire would be a source of entertainment for her, especially if that fiery personality trait Sumire's showing could be used against her.