It seems it's not so much a birthday, but "the day that Ran became a shiki". When I told Yukari before...Here you go.What do you mean? Not inviting Reimu since she devours food like a wild animal is one thing, butSo then, Chen, have you gotten a present?What?is what she said.
Hmmmm..... hm?Why weren't we invited?Who's the wild animal and who's the idol?...They haven't had one before this, right? And just what is Ran's birth date?I was wondering what a birthday party is.But why are they having it now after all this time?How could that old woman Yukari not invite Marisa-sama, the idol of Gensoukyo? She just doesn't get it!Oh well da-ze... Huh?You're asking "What's a birthday party"?Don't play dumb, you walking disaster area."You're working her too much, even if she is a shiki. If you don't reward her for her efforts, she'll get depressed sooner or later","But when I praise her, she gets nervous.
...Well then, maybe I should have a birthday party for her?"Has there ever been a party that we've been at that ended peacefully? Who would invite us?What?Yeah. Well, you know, today, you know, they're having a birthday party for Ran-sama. And so-A birthday party is a gathering where everyone celebrates their happiness over that person having been born and the preciousness of that person's being alive.
I guess you as a shikigami wouldn't really know what a birthday party is.