i can't see a reason for an elf to capture a demon or devil except seeking power
Well, like I said, revenge for something. Perhaps a devil hurt her, or her family. Although, if the elf thing is the issue, then we could just make her a normal human....
The problem with the "seeking power" thing is that it means she won't really be trying to
hurt Sakura, as such, just to experiment on her, and that gets in the way of what I'm aiming for with the scene.