Aisa is the little Shandorian girl who has the ability to use Mantra since she was born. I think her ability is actually to be able to hear the voice of all things, which was mistaken for observation Hali (mantra). I'm not sure why Oda would have focused on this aspect of Aisa so much in the arc. It might be a stretch to guess that she is the ancient weapon Uranus... but I think it would be fitting for one of these Shandorian to be Uranus... like how a mermaid is Poseidon.