I re-watched the last scenes just for fun recently and then I realized something. Kozue is sit next to the piano and that indicate their relationship had evolved but something bug. Maybe that because I only watched Miki episodes twice and so I probably didn't get/forget important details, but that scene gives me the impression only Kozue take an effort in their relationship since Miki pretty much only liked Kozue (?)  when they played piano together during their childhood I feel like Kozue only get his attention now by playing the piano (instead of sleeping with every boys around) and that annoying me because I think both should take an effort in their relationship but then again I get the impression I just missed important part of Miki's character and that he probably get enough character development to stop idealized  his childhood and see women only as pure (Anthy) or impure (Kozue).

So my question is what happened to Miki that make him grown up and made change his relation with his sister? Is that happened during episode 26? Does he took effort in his new relation with Kozue?