FF7 Neo Riddles

[champagne supernova]

So fraternal twins apparently are two eggs fertilised by two separate sperm. Judging by the hints, the answer must have 2 materias, which are completely opposite. However, I don't see how mastering materia gets involved if, by the definition of a fraternal twin, the 2 materias come from different sources.

EDIT: Thinking Full Cure & Ultima. Both originally start off with no ability, but reduce your stats (hinder). As you level them up, you can use the spells.