I'm not understanding what you mean when you say "the top is even all around", I see a sweetheart neckline on both the costume and the pattern. It's a very good match in my opinion. Is it the back of the pattern that is confounding you? the character has that sleeve-holding-on-to-nothing that artists like to draw in anime :/ but at least there is some bodice back to work with.
I would actually do a muslin of the back and sleeve. Cut and sew as the pattern is, then cut down and add a facing to get that shape in the back. This means having a tiny 1/2" wide shoulder piece to actually attach the sleeve to, meaning it will wear more comfortably as well as stay put on your body.
If I'm wrong about your questions please elaborate.