I'd like to think that maybe Sora's just waiting for Sena to mess up to make her move, but I'm not too sure about that from what I heard and read without reading the manga. She has been quite a bit of a jerkass, though I can understand why she can be when all she just wanted to do was create a club just for her and her childhood friend when all of a sudden a rich bitch who's good at everything (who also a childhood friend and was set up for an arranged marriage by the fathers), a genius ditz, and a person who would do anything for him shows up and becomes competition for his feelings when all she has is childhood friendship. I would imagine the plagiarism was something to impress Kodaka with hopes anyone wouldn't find out, but that kinda backfired on her.
I'd also imagine Rika is savvy enough to know that she doesn't really have a chance compared to Sora and Sena, so she just tries to shake up the status quo to get a reaction out of Kodaka just to gauge where he stands in the whole situation.
Though whomever he chooses, he does have quite a bit of choices to go hide whenever he gets in an argument with that person. Of course that's assuming everything turns out okay after the decision is made and he doesn't set off any bad flags for anybody else. I suppose he can always go to confessional at the least.