Which leads me to my next thoughts, namely that I did like the story a lot, it's heart-wrenching, but I'm torn on whether I can see this as being in-character for them. Rika's thought process is very canon; this is exactly how she thought after she first made her wish. But I wonder if she would really be this cruel to Ren. She did decide to take things into her own hands with her childhood friend, by breaking things off, for that girl's supposed best interests, so makes sense she could do the same with Ren. I think I like to see her as a kinder person than that though. Would like to think that she's grown since she made her wish, since her time with Ren.
I think the focus is more on Rika's own insecurity and self-loathing; she doesn't believe that someone could actually fall in love with her, and she's afraid of hurting Ren like she did her ex-girlfriend. So in her mind, even though its cruel to reject Ren's feelings, it would be crueler still to force Ren into a relationship with her through magic, so it's better if she breaks things off now and lets Ren hate her so that she can be free to fall in "true" love. Later story events have shown that Rika still kinda hates herself over her wish and she's never really gotten over it, though she's very good at hiding it.
Thankfully Hinano helped smack some sense into her dumb kouhai. RikaRen are beautiful destiny.