Even Zanna and the rest of the top powerhouses in the world could recognize Alister's identity as an otherworlder, let alone Fantasia. After all, Alister didn't actively hide his identity as an otherworlder.
However, Fantasia had mistaken the origin of Alister's authorities and misunderstood that Alister's authorities were due to the world that Alister came from. In reality, Alister's authorities were all from the world travel simulator system.
Due to that misunderstanding, Fantasia wanted to kill Alister and search his soul to trace the origin of Alister's world and discover the secret of Alister's authorities.
Although Fantasia was a top existence even in the God Realm, she barely had any divine authorities and the ultimate authority above it was just a myth to her, let alone Alister's supreme authorities.
Because of that, gods such as herself value authorities since it could give them an advantage over enemies in the same realm or power level as them.