User blog comment:Crimson Storm Mich/Future Units Preview v2/@comment-30462510-20170322150923/@comment-31529105-20170323021849

She seems to be on of the JP exclusive units whose story is tied into the summoners ark, belonging to the Elgaia federation An example wiulr be Reda' omni and her 7-star evolution. More info here: http://bravefrontierglobal.wikia.com/wiki/Mel_(character)#

Because she has no UBB, the has no actual use for most content, so she might be a helper unit for one or more stages in the summoner's arc. I woudn't know for sure since I don't play BFJP.