Yeah, currently the one with the best chances (assuming this does end with a romantic pairing) is Kanase by a long shot, since she was key to setting up the premise initially, and we spent a good bit of time in her head.
It is not normal to manipulate others to get what you want in that way, or use others and then insult them behind their backs. Plenty of people like that exist, but that does not set the bar for healthy or acceptable behavior. It's just emblematic of the ugliness humans are capable of. Some kids...
Until then, my theory is that she is literally a child using magic to pretend be an adult, and sneaked out. Pretty sure it contradicts some previous scene, but it legitimately makes more sense then the alternative, currently.
That's some pretty shitty talk from her co-workers. Have they really not noticed she's not the type to want to have these conversations, or have her sex life be treated as casual info to spread?
Her showing up there was pretty sus. I lean towards it being "Oh here's a good spot to run into her as usual, ah wait she looks sad/frustrated, new plan" rather than full on creeper though.
Did she break out of elementary school in the demon realm? I'm being entirely serious here. Is her backstory literally sneaking out of school, and her parents are currently panicking looking for their little Ruu-chan?
The point of my response was to highlight how your description minimizes what happened and why it happened. Emphasizing how it's "what kids do", when plenty of kids don't do that, and how it was the "image he made in his head", despite that image being very intentional on her part. Other...
She would eat you alive. A smile while doing it. Genuinely though, a person like her needs a lot of therapy. They would have to recognize that the way they are is problematic in the first place to change.