Materia is activated as soon as you attach it to a slot. On that note, it's been quite a while since I last played FF7, so I might have been giving you some false information. HP/MP Absorb work when attacking with the linked Materia. IIRC, if you want to absorb spell damage, you need to put Added Effect + spell materia in your armor. So yeah, my apologies. Needed to do some digging myself as well. blooddrinkerS: Read the board rules. First warning.