>>9726788>Yukine was intended to be a Main Heroine in the final game, but her story wasn't up to par with the others and she was relegated to sub-heroine.
According to Maeda, Yukine's route was going to be a really sad route. He said he didn't know how to end it, and so they discarded it. Honestly, just by reading that interview, I could tell it was a good route. I have no idea why wouldn't they include it.>>9726895>Also, if you talk to Tomoyo but don't start her route she'll make an appearance during Yukine's story.
That happens with almost every heroine. Depending on whom you focus, that girl will make an appearance in Yukine's route.