S1eth said:
For Cirno, alternate_persona and opposite_persona could mean either her using fire instead of ice or her being intelligent.
Seems reasonable. They clearly meet a definition of "opposite" for the character.
This can include even genderswaps and adult versions.
Not as fine with that. That doesn't really fit the spirit of "opposite" to me, though in the case of Cirno you can make an argument for adult. I think that should be specifically exempted from the tag in its wiki description.