I only need one image:
And we cannot forget the brownie points to Noriko; for opening Touko's heart and prodding her to look deep inside on how Touko herself thinks of Yumi. I don't fully remember the words, but "the single thing that matters most between souers, is how much you like each other."
I also thought the preview spoiler was silly, but season 4 previews have been quite spoilery, anyway..