The original case report is
here.
I cross-checked the original by checking dates on the reviews, which conclusively establishes that the original fic was posted as far back as 2006. The date on the
tumblr screencap shows that it was posted approximately 2 weeks prior to today's date.
I did some phrase searching and it does indeed appear that aside from the POV change, the wording of the copied fic is very similar to the original and therefore constitutes plagiarism.
As I am not a tumblr user I could not contact this author, but I suspect such contact would be superfluous given the rather open and shut nature of this case.
I shall therefore add benihime1231 to the list of known plagiarists for one year, with an eye to possible movement to the indefinite list should the story fail to be taken down by the author or by tumblr.