I agree it can't be Serini, but some of the points being made by people in the Serini camp (namely about how it'd make sense for the character in question to have already been introduced or to be introduced shortly if they're to be an ally during the first half of this book) make me think it might be Orange. And there shouldn't be that many one-page characters that could be Orange, given their implied size and (maybe) number of limbs in #1189.