Restia is Kazehaya Kamito's contracted spirit, though she's also known for being able to transform into her sword form independently without needing a formal contract—something pretty unusual for a spirit. She's a high-level darkness elemental who appears as a young girl, which is her default state.
Her elemental waffe form is where things get interesting: she transforms into Vorpal Sword, a jet-black demon blade that's supposedly capable of piercing truth itself. Fans often note that her ability to shift between forms on her own and let other people wield her without a contract makes her pretty versatile compared to most spirits, even if that flexibility comes with its own complications.
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