Originally Posted by Shadow5YA
I expected Rin to grow more than this. Something is wrong when even Kuro is bigger than her...
If Rin grew to anywhere near Aoki's image of how Rin turned out in the last few pages eg pretty much just a normal adult, then it would make an easy ending - as it would be a no brainer for Aoki to decide (if Rin really grew to become just like Aki then he'll just take her on the spot), this is probably the final hurdle he'll have to face because he would really have to question what's his feelings and expectation towards Rin are. Also the situation on Rin's side is the same - she was living under the impression that Aoki won't return her feelings partly because she's a child and was hoping that with age she would grow up to be an adult which then Aoki would accept her, so her not (physically) growing would be a pretty big mental strain on her too. So at least I think that's what the author is trying to do here, with the waiting/legal age thing out of the way what would happen to their relationship when things didn't turn out to what both of them are hoping for.
Of course I could be wrong and the author is just trolling us.