I didn't say she was a living spirit, I said she used to be a living person. I do believe Hector mentioned that. Just to be safe.
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Hector said Ursula was a 'casualty of Ragnarok' and always refers to her as a 'she', 'her', and 'woman'. If that doesn't make her female, I don't know what will.
And I guess that although Seth is Ursula's opposite I guess they are only opposite's in their beliefs and such. I mean, they are almost one in the same in a sense since one cannot exist without the other and stuff.