I agree with PikaPandaPan on the pattern. I've recently made a cape but as I'm part of a history group we know a bit about what we're looking for.
For this one I would recommend buying the first pattern that she linked (http://www.simplicity.com/p-2272-mis...-costumes.aspx
) then following it to make the grey one in the top right of the 4 pictured but leaving off the hood and sleeves. it's the closest to it.
with a bit of imagination you could get it to look like the one in the anime.
if you're unsure about it I recommend getting some cheap or scrap fabric and making a test one out of that first. if it goes wrong, maybe cut too short or doesn't fit right or look right you can fix it without worrying that you've wasted your good fabric.