I liked this story, but since you mentioned research.... (Usually I separate out the part of me that is researchy from the one that enjoys a good story when reading fic.)
基本的に (Fundamentally), the Heian Court and the Edo Period used the same calendar. There are subtle differences (mostly having to do with astrological reckonings), but they wouldn't have counted much for anniversary reckonings. (Some Heian courtiers, and the law codes, sometimes refer back to Chinese systems that were a little different--the "10-day week," for example, or other month divisions--but those weren't the sorts of things you'd look up in your hand-calendar. Well, they'd be written in for you, if you needed them. ;)
As far as I'm aware, although it was important to mark when someone was born (for astrological calculations) if you were high-born, the Heian Court did not celebrate birthdays per se. Death anniversaries were important, but that's a whole different (Buddhist) kettle of fish. I have no clue about Edo-period customs, since apparently no one went to temples to celebrate birthdays.... Well, none of the ones I've had to deal with, anyway. ;)
All of which: makes no difference anyway, to a satisfying story. (It's not like Hikaru no go is spectacularly accurate for the Heian Period anyway, so I only mention this in case of your own curiosity, not as nitpicking. Heian-picking?)
no subject
基本的に (Fundamentally), the Heian Court and the Edo Period used the same calendar. There are subtle differences (mostly having to do with astrological reckonings), but they wouldn't have counted much for anniversary reckonings. (Some Heian courtiers, and the law codes, sometimes refer back to Chinese systems that were a little different--the "10-day week," for example, or other month divisions--but those weren't the sorts of things you'd look up in your hand-calendar. Well, they'd be written in for you, if you needed them. ;)
As far as I'm aware, although it was important to mark when someone was born (for astrological calculations) if you were high-born, the Heian Court did not celebrate birthdays per se. Death anniversaries were important, but that's a whole different (Buddhist) kettle of fish. I have no clue about Edo-period customs, since apparently no one went to temples to celebrate birthdays.... Well, none of the ones I've had to deal with, anyway. ;)
All of which: makes no difference anyway, to a satisfying story. (It's not like Hikaru no go is spectacularly accurate for the Heian Period anyway, so I only mention this in case of your own curiosity, not as nitpicking. Heian-picking?)