She was pretty early getting interested in Jirou. At least until somewhere in the early thirty chapters she was drawn between the two boys, slightly leaning more towards Jirou, which is why she wasn't that heartbroken when Minami rejected her as he had never had feelings for her, and he could...
She's a teenager, not to mention she hadn't fully decided yet, as much as she wanted to vote kyouka, she needed to look at the bigger picture also, and either ren brainwashed her or that ability was so good that it swayed her vote in her direction
She didn't change, she hadn't decided who she would choose yet, and while she felt bad about it, either ren must have manipulated her mind or had some kind of extra broken ability we don't know of yet
don't disagree with Akane being attractive and Minase being about as attractive. And we can only wait to see when both of them become Yuto's women and who else will join them.