Unable to see, but hits every time.- materia has no eyes, and magic materia cannot miss. Summons don't miss, but summons have eyes.
Power unmatched, it soon sounds your chime.- Magic is very powerful, and death will "sound your chime" in one shot unless you're immune to it.
From one to sixteen, it can come in,- The amount of materia you equip is based on your equipment, and the least is 1 and most is 16.
Eight sets of two, the maximum.- If you equip items with 16 slots linked together, there are 8 sets of two.

KotR is really close because it is a summon materia, which matches every part of my riddle except the unable to see.