The fact Akira likes sensei from the beginning, since when she was still a boy, was apparent to me and it’s still a surprise seeing it genuinely escapes a lot of people.
As for Kanata, I see it as he only has a temporary transformation as long as he has a regular help from the candy, so I don’t really see his case as back transformation and more like effect wearing off. Haruki and Akira is semi permanent though, as far as I understand, so, if Akira does turn back because of the thought (and not just running out of energy because she refuse to drain sensei), that’s what I see as back-transformation.