Perhaps a bit outlandish but what if Anima is the corrupted soul of the WoL from the 13th shard? And either Fandaniel summons her in an attempt to stop us or we summon her in an attempt to rejoin our souls before fighting Zenos?

It fits the light/dark and rejoining themes of the entire Ascian story, its also a mirror to hydaelyn/zodiark and is also the kind of oblique head fake the writers like to do.