The form that Spirits undergo in Date A Live when they are put through significant mental stress and negative emotions. Visually, their Astral Dress changes as well to make an "Dark Persona". They also act much more differently, specifically become more violent and their destructive power increases.
They are actually the natural form of sephira crystals, but the Spirit of Origin changed them through lots of trial and error to make them compatible with a human vessel.
List of all of the inverse/reverse spirits:
- Honjou Nia (Inverse)
- Tobiichi Origami (Inverse)
- Yatogami Tenka
- Himekawa Yoshino (Inverse) (does not actually appear in the story)