Adapting Materia from their original role in the videogame proved rather tricky. From a fluff perspective, they're raw crystallized magic. From a mechanical perspective, they provide the world of FF7 with spells you cast mid-combat, and yet they also serve as interchangeable equipment upgrades. I tried to reach a compromise that was balanced, made sense within the setting (omitting the materia that increases the amount of coinage you find, for example) and still stuck to the same underlying mechanics of materia slots. Oh, and it also had to still be fun.
The Materia power is identical to the 4-point version of the Device power, with the following restriction: The power points must be used to create a single ability that takes a full action to use and has a duration of Instant or Instant (Lasting). Additionally, Materia must be mounted onto a device's materia slot (see below).
Device Extra: Materia Slot
The device in question can hold one Materia, letting you use that materia's ability as an Alternate Power. The Materia's effective PL is limited to your device's PL. This Extra can be taken multiple times.
Device Extra: Linked Slots
A pair of unlinked materia slots on the device become connected. Materia stored in these slots may be used together as though they were combined via the Linked extra, assuming their powers are compatible.
Feat: Materia Attunement
You may attune yourself to a Materia, allowing you to use it whenever it's on your person rather than having to equip it in an appropriate slot. You must first concentrate on the materia for a total amount of time equal to half it's power rank on the Time and Value progression table. You may only be attuned to one Materia at a time.
Players can also use Support Materia. This type of materia always costs 1 point per rank, and grants one of the following Power Modifiers to any materia in a linked slot whose power is of equal or lesser rank:
-Added Effect (Links paired materia to Device's power)
-Turbo (Paired Materia gets +2 to effective rank, gains the Fades flaw, recharges by not being used for 8 hours)