Or does it only boost the character with "Black Resonance"? If someone could let me know how exactly this mechanic works, I'd be thankful!
Black Resonance only increases magic damage for Black Magic spells when you have other party members with Black Resonance. So, selecting Black Magic or B/W Magic as a secondary job ability will not increase black magic damage if you only have one character with Black Resonance. Once you have multiple characters equipped with Black Resonance, each character will have their black magic damage increased as follows:
- 0 allies: 1x multiplier (No effect)
- 1 ally: 1.1x multiplier
- 2 allies: 1.15x multiplier
- 3 allies: 1.2x multiplier