I'm starting to think Brandish might be Layla Heartfilia or Anna. Remember the Eclipse Celestial Spirit arc? The effects of the Eclipse Gate caused the 12 Zodiac Keys, after closing it, an alter in their memories and appearance. Layla and Anna opened the Eclipse Gate 400 years prior to X777. The Eclipse may have done alters to either of the Celestial Spirit Mages and, under Zeref's wing, joined Alvarez Empire under the identity of Brandish, presumed dead by either's loved ones. Just a thought.