I want it to be more than just a glowy stat stick. I'd want it to enhance other abilities or attacks that we have.

Extreme examples just to give you an idea:

Blm relic grants 50% reduced MP cost during astral fire.

Smn relic doubles all DoT durations.

Pld relic reduces or removes damage penalty during shield oath.

Now I obviously don't expect the relic to be that extreme, but I'd want it to be something that changes up gameplay or adds some sort of significant boosts outside of boring old stats.