I agree about the volume 2 trio, but Yurine's interaction with the track team (and Ai too) was an important step in her opening up. The end of chapter 5 pretty much sums it up: by going towards the others, Yurine remembered that being alone was painful, and Ayaka was the trigger for that.
Apart from volume 2, every arc served the development of at least Yurine; and while it's true that Ayaka only started mellowing out to Yurine during the gardening arc, that evolution probably wouldn't have happened if Yurine hadn't opened up first. So volume 1 as a whole did indirectly serve the main couple's development. It may sound a bit far-fetched but that's how I see it.
(also, in chapter 2 Ayaka wasn't going to bite her but to kiss her I think. ^^")
last edited at Sep 12, 2015 11:41AM