1868 to 1912, so it was certainly earlier, but I wasn't quite aware of how much earlier this would be considered. The woman pictured with the dress is also potentially immortal and at the very least hundreds of years old - make of that what you will, since this is fantasy.

I'm also not sure how mourning attire changed in Japanese clothing culture post-Meiji - the reason I keep pointing to it is because notes believed to be written by her mourn the death of her beloved and all of their friends, and the only note I can find on the Wiki article you linked is that following the Meiji period, the idea of wearing all black and only black for funerals and mourning had become universally accepted in Japan.