Editing Macchiato Monsters: The Stygian Library (section)

====About Reagents and Faith====
They function similarly, again as "armor" against spellcasting HP costs. A character can only use one or the other: either you fuel your magic with gleaming orbs and your own Nietzschean will to power, or you channel it through a higher cosmic focus and social support network.

The advantage of Reagents (whether mixed powders or thrumming scepters) is that they're impersonal: you can just get more of them if you run out, even buy them at the right market, and some have a variety of quirky side powers to spend that Risk Die on as well.

Faith involves some social context like a code of conduct and people you're responsible to, and recovering or improving the singular Faith die requires putting your time and devotion in for them. If you have a Faith die, you can roll it for a few other things in addition to spellcasting costs:
*Roll the Δ (and risk stepping it down) to get advantage on an action in line with the faith.
*Spend an hour in devotion/prayer/gun kata/whatever to roll the Δ and heal that many HP on yourself or amenable others.
*If you're not wearing armor, use the Faith die as armor.