Hi, Watcher here. Thought about putting discussion about Rhyme and Cassie here, so here I am.

I don't think Rhyme would necessarily dig into her past, specially if he doesn't know that there's something to dig; as it is, he's pretty busy figuring out his past, with the amnesia and all. That said, from how our thread's developing, he's picked up that Cassie's definitely no normal little girl, and might try to befriend her if he sees her more than once... if she hasn't tried to kill him before... ah, scratch that, he'd probably try even if that was the case, since he would be intrigued on why such a person seems to have so much hatred. So he'll probably do some digging, but not historically, if you get my gist, both because he wouldn't think about it and because he's still fumbling about figuring out how to dig into history. Maybe he could convince her there are good people in humanity, and maybe not. He'll certainly try though, that's his thing.

That said, not sure where any interaction between the two of them will go... so maybe it's for the best to just see how the thread rolls. Unless you have ideas?

He'll probably not persecute her, yes, but he'll definitely try to stop her when she tries to kill people, if he ever gets wind of her attempts. He'll probably be conflicted over whether he should capture her for the authorities, considering he probably can't stop her every time...

Mrm, yeah. I guess we'll see how they react to each other, then~

I'm not sure what you mean by a background? The general plan was to have him think, or consider, that he was the person he imitated, and consider how much things have changed from when that person operated--- and how, while mutants aren't quite persecuted now, there are still people suffering, all while he has a feeling that he might not be that person at all. In the end, he discovers that that person was not him, but merely someone that he admired, but that's okay, as he decides to continue that person's legacy, but at the same time deciding who he is apart from that. I'm not quite sure if this is what you were asking for, though...

Cassiopeia

Oh, that's a really good angle.

What I had in mind for Rhyme's past was not experimentation, per se, but he was definitely used for his unique abilities, so perhaps the difference is negligible. The main problem is that Rhyme's time period was... a hundred years ago, when Eos was still a monarchy, so the timeline might be a bit of a stretch, unless... they were a group of nobles that survived the upheaval of Eos turning into a more democratic sort of government, and they'd continued on their heinous machinations behind the political curtain, ending up maltreating other people and creating Cassie's situation. Could even make for a competing big bad for the Grimm Troupe, haha, and might even be a good reason for unlikely team-ups.

To be fair, Rhyme is looking for his history because it's kinda missing from his brain, but well, indeed, Rhyme would be the sort of person to seek the truth even if it would be painful, and that is probably the divergence between him and Cassie.