[stubby42]

Mikuru is probably Japanese, or at least looks it. Her hair is described as "brown" in the novels...

Well are you talking about ethnicity or country of birth? unless the subs are wrong she says

Spoiler for since were not talking in detail yet:

so this is the traditional dress of this country

Which implies shes not from Japan.

As for the idea that she'd be unfamilar of fire works, I suppose its possible but to be honnest technological changes and cultural changes dont really work like that. Its a cultural activity practiced the world over, technology only disapears when something better replaces it, fire works serve no pracitcal purpose so nothing is likely to replace them or something happens that causes us to loose knowledge (think Roman empire to the dark ages) but that seems unlikely because our ability to produce information and record it has grown dramatically.

I thought someone discribed Mikuru as a foreigner once.

Ok, that might make more sense I really want to start reading the novels but I dont have the money to buy them.