To have True Faith at all, a vampire must buy a 7-point Merit (p. 494 of V20 Corebook). It is also mentioned there that it is possible to lose the rating in True Faith (and, therefore, increase it). But how does one do it? Do I pay for it as for Abilities? Or as for... what?
True Faith, as described in the V20 supplement Hunters Hunted 2, is a Numina. A dot of True Faith costs 7 freebies at character creation, and you cannot start with more than one, so that's your Merit cost right there. You raise them by spending (Current Level x 7) in XP.
Here’s the rules on how you get permission to raise True Faith, from that supplement:
True Faith is increased by acts of devotion toward the character’s revered higher power or cause. Additional points are awarded only at the Storyteller’s discretion, based on appropriate behavior and deeds. The Storyteller should closely consider the Faithful’s actions during the course of the story and inform the player when he believes that it is appropriate that next level be purchased.
Emphasis added. Now, vampires don’t ordinarily gain access to Numina. And it’s arguable that as a damned creature that drinks blood, you're unlikely to be granted permission. But Storytellers may have more mercy in some games than others, and grace is permitted to even the Kindred. So while my instinct is to say, “You’ll probably never actually get to raise it,” the rules are there to do so.
DAV20 book has an interesting alternative answer on page 392.
- You don't pay points to have True Faith at character generation.
In game terms, True Faith does not cost Merit or experience points; it’s a player choice with Storyteller approval.
- Neither do you pay to advance in True Faith.
Increases in True Faith should come only with Storyteller approval as a manifestation of the story being told. There are no systems to abstract what reflects a gain or loss of this sort of faith.
It might apply stronger to the V20 because Hunters Hunted 2 is a different game, but some Storytellers might prefer the latter to keep all characters on more or less same level of power by forcing them to spend points.