This is all speculation on what's to come in the rest of the story.
I wonder if Hebikawa is going to try to steal Keisuke from Shizuka, not realizing that Keisuke already knows that she's a mesan girl. Not sure why she'd be motivated to do that. If she is going to, then Keisuke will probably have to get used to being around Hebikawa because it would be suspicious for him to want to distance himself without letting it slip that he knows her since he isn't actually dating Shizuka, and that will be great for acclimating him to being around pretty girls. Meanwhile, Shizuka is going to gain a lot of experience from talking to Hebikawa (aka the final boss) even though Hebikawa doesn't even like her. While all of this is happening, Hebikawa is going to grow a genuine relationship with Shizuka that makes her rethink her manipulative personality and become the kind of girl she wanted to be when she was growing up. She might even start to genuinely like Keisuke, but that seems unlikely to me.