Items with 5 Materia slots?

[MistakeNot]

1. Take any of the older 4 slot ones, fill it, and then overmeld just ONE TIME and get the achievement. (I've never had it work even once, but if this was the only option I was prepared to accept it)

If you are just interested in the achievement, then this is by far the simplest and quickest option.

[MsQi]

The great irony here is that higher grade materia are much more plentiful, with many ways of obtaining.

It'd be awful nice if there were ways of buying the low grades as well. Especially for anyone mad enough to try to complete multiple ARR relic weapons.

last I tried you can buy really low level equipment and go kill low level mobs for a few minutes and have like a whole set's worth of low level meteria.

[Hasrat]

last I tried you can buy really low level equipment and go kill low level mobs for a few minutes and have like a whole set's worth of low level meteria.

Fair enough, but, still more rng involved than just picking the things you want/need.