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As Sylphy Spirits and Familiars fought with everything they had, one of them was left out, Alice, the representation of Sylphy's System. Even after she made a familiar contract with Sylphy and her existence suddenly became more defined, she was still an alien being from this world, not really a spirit, not really a living being, so she couldn't really "define" her form yet, and getting out of Sylphy's soul would also be somewhat dangerous in many ways, as it could even risk her losing the System at all, so she really didn't wanted to come out.
Check "The Protagnist's Sister Is Actually the Strongest"!