All fanfic by its very definition is derivative. However, within those derivations are I think clear delineations of quality. I consider Tira to be among the highest, so I thought a comparison would be complimentary. Had I compared your writing to JKR, I suspect there'd be no issue at all (not to equate Tira with Jo, but I hope you get my point).
I've always admired your drabbles, but this story really impressed me. I don't comment often because, frankly, most of the stuff out there IS derivative in the worst sense of the word, tired and old hat. This is one of the few refreshingly original plots I've read in a long time. Which perhaps I should have said at the beginning. ; )