I feel like the aspect of Yukine’s route which makes it stand out the most isn’t necessarily her character but more so the fact that her story presents a theme and plot device which seamlessly introduces the greater plot of Clannad which (If following the order of the bookclub) we’ve seen small glimpses of thus far.
I know @Pepe mentioned that the light orb background story after the credits roll isn’t necessarily part her route so to speak, but the plot device stems from her role in the story, albeit minor. I really want to emphasise that as part of what I love about this route so much.
Allow me to clarify what I mean.
Yukine may be a minor character who doesn’t have much presence and her story isn’t exactly grand scale or very dramatic either (in the VN at least. Anime was a bit… edgy). But her being the hostess of this reference room opened the opportunity to show the reader a character who has access to all sorts of bizarre information and items (magic spells, confiscated belongings from students, and old thrown out books ect)
When coupled with her story, a girl who brings other happiness and but has yet to find happiness herself. Taking both in consideration gave a very subtle transition to the scene explaining the light orbs after the credits rolled.
What I like about this is that it transitions perfectly into Yukine giving us the small piece of exposition at the end after the credits telling the reader all about the light orbs. It may be early on, but it emphasises those light orbs are very important
The fact that her story complements what the orbs represent, paired with (albeit kind of conveniently) her being someone who has access to strange information like that, in my opinion is quite clever writing.
To summarise, its less about Yukine, and more about what her role presents to the greater story. Having read After Story already now, it makes me appreciate what this route does for the novel in the long run.
As a stand alone route, it can be seen as poor. But otherwise I argue it’s pretty stellar.
EDIT: Kotomi route spoilers They could have easily had something like this take place in Kotomi’s route for example. considering she is a bit of a bookworm and could likely fit in just as well. But I feel like Yukine was the selected character because she was the ‘most relevant’ to get the point across from a writing standpoint.