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If Hydro's new form seemed to be capable of staying in the mortal realm, or simply the surface, it meant that she had acquired something that most gods seek, an ideal mortal vessel.
It has been explained before, but to resume it, any type of God, the stronger they get by raising Ranks, the harder it is for them to maintain their existence in areas that lack a dense amount of Divine Energy.
This is because their existences are simply too strong, the entire world and its attributes begin to be pressurized by their existence if they stay too long on the surface, and to lessen this burden in them and the world, they must spend Divine Energy.
Of course, the more weakened a God is, the easier it is for them to wander on the surface without much burden. And Gods such as Living Deities up to Rank 8 are quite safe on the surface, needing very little Divine Energy to sustain themselves.
Check "The Protagonist's Sister Is Actually the Strongest"!