MYSTICS Team Ability
When a character using the Mystics team ability takes damage
from an attack, the attacker is dealt 1 unavoidable damage. This damage is not an attack.

ULTIMATE VAMPIRE:
I, Vampire can use Hypersonic Speed, the Mystics team ability, and his powers can't be countered.

EMPOWERED BY CAIN'S DEMISE:
When turning the dial, if this click is revealed due to damage taken from an opposing character's attack, stop turning the dial. This power can't be ignored.

Scenario:
One of my characters attacks I, Vampire at a moment when he can not use the Mystics team ability. But my attack causes his dial to be moved to his stop click EMPOWERED BY CAIN'S DEMISE where at that point he can use the Mystics team ability.

Question:

Would my character be dealt 1 unavoidable damage, even though the attack was done before I, Vampire could use the Mystics team ability ?

No, because the character did not have access to Mystics when the damage was dealt.

Thanks Wolverazio.