Joou no Hana has a pseudo-Chinese (?) setting of "long ago" but is it properly based on a period in human history? I don´t see it. If so then which one is it?

A Song of Ice and Fire, Berserk, Conan the Barbarian, Guin Saga or the (mostly) non-magical Arslan Senki aren´t historical fiction, as that period of human history never existed.
Am I correct to assume that we have a similar case here? Let´s figure the proper genre for this series out, or the lack of it, once and for all.

I also read EU/US comics and am a librarian.
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