Don't worry Kanny, I have a theory as to how things might play out so that Kanae doesn't leave Potte and friends.
Spoiler for Kanae's Final Gambit:
Potte: Kanae-chan, I can't believe you're graduating soon... I'll miss you so much...
Kanae: Don't worry, Potte-chan. I'm not.
Potte: Huh?
Kanae: I flunked out of all my classes on purpose so that we can be together next year!
Potte: Ehhhhh?!
Kanae: Ano ano, eto eto... I hope you're not mad.
Potte: I'm not mad... umm... now that I think about it, you do finish your homework faster than the rest of us do at study sessions... I thought that was just because you're our amazing senpai, but could it be that you're cutting corners, perhaps?
Kanae: Yep. I don't write anything down on my homework anymore, I just draw pictures of kitties~
Potte: ... umm... so how did you fail Gym? You get graded there for participation...
Kanae: I started throwing basketballs into people's faces and tying their shoes together when they weren't looking! I don't ever pass in participation because I always have to sit out! *beams*
Potte: ... A part of me doesn't want to know, but that student in Driver's Ed that drove off a bridge during their driving test...
Kanae: Yup, that was me! I certainly didn't pass that exam, teehee!
Potte: Everyone thought that was an accident, but it... wasn't, was it?
Kanae: Nooooooope~
Potte: Kanae-chan... you'd... go that far for me?
Kanae: ... hai... Potte-chan...
You heard it here first, Kanon. You heard it here first.
I wish the false information I posted on the first page about this series being two cours had turned out to be true, I love Tamayura too much to see it go. ;_;