Hey, don't know if this has been answered before, but do you

[Vertical Inc]

Hey, don't know if this has been answered before, but do you know if there's a reason that the first volume of Twin Spica is only available on Kindle Fire HD in the UK amazon store, when the other volumes are available on other varietys of kindle?

No idea. We suggest you contact Amazon UK about that, as we have not and never have requested such a meaningless restriction.