It would be an interesting turnover if the "plain girl" Karen somehow manages to snatch up Touma. I didn't notice if there was a note, but "karen" is "beautiful, pretty, neat in appearance" in Japanese, which is the ironic part.
I do like how this series is so... amoral, I guess? We get taught that love is a higher good, but love can be destructive or dangerous. At the same time, in my view Touma isn't any sort of villain, more of a force of nature. For some people it helps them, for some it hurts them, but Touma doesn't seem to be really at fault to me. It's not like they can't refuse her - she doesn't force anything.
I actually really feel for Karen, I kinda feel like a side character in life right now and feel like I don't have anything special... I think Touma was a trigger but these feelings were there before, just Touma gave her the ability to fight against that. As to whether fighting against that is good or bad, well, we're all characters of our own creation, that's what existential freedom is all about.
