One Last Push!
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As Rita grew stronger and evolved her magical abilities, her "Gates of the Underworld" Spell, an ultimate Spell that consumed all her Malice Essence naturally become stronger as well, as did all her spells. However, to release its true potential, she first needed to transform using her Divine Fusion Skill and channel the power of the Void Dragon Spirit Soul she was cultivating within her very being.
This power was one of immense strength, but it came at the cost of consuming her life force rapidly. Without Elayne's domain, Rita would have already dropped dead from summoning this enormous gate, an upgrade that didn't led to the Underworld anymore, but to a completely separate realm.
One where only the Void, and whatever resided in it existed. And that thing, what resided within the void, it moved. And it acted. Unable to find a logic explanation as to where exactly this thing came from, Rita conjured the spell.