>>542382156
Until the end of her AQ, Furina is technically still a part of Focalors: she embodies her "mortal and carefree" self, the image of how she pictured real humans, or how she wanted her fellow oceanid Fontaininas to be and feel; she was created to distract Celestia while Focalors was accumulating indemnitium so that she could have enough power to guillottine herself.

So while Furina is human in spirit, she's still an immortal doppelganger until the very last breath of Focalors. After that, she becomes a full human, just like every other Fontainian, and gains a proper vision for herself.