Black Mage

[Aysen]

It would be cool if every time a BLM spends an Umbral Heart the entire party received a small amount of mana.

Practically, it could be something like all party members recover 1% of their mana. Roughly 3% every 30s seems reasonable. Can tweak the numbers. Maybe 2%. Who knows.

Lore-wise it could be something like, shatters an Umbral Heart and directs it's energies to bolster the party's mana and calm the torrent of energies surrounding the black mage while affected by Astral Fire.

Wouldn't be too far of a stretch lore-wise, would make Umbral Hearts more than a gimmick and would give BLM party usefulness. We're already considered "mana batteries". Might as well embrace it.

[Kabooa]

Wouldn't be too far of a stretch lore-wise, would make Umbral Hearts more than a gimmick and would give BLM party usefulness. We're already considered "mana batteries". Might as well embrace it.

I don't disagree with the utility, just the execution.

That amount of MP is likely to be completely wasted or insignificant where it matters. It's weaker than a bard or machinist, and it's not strong enough to be useful when it's needed most.

Speaking personally, I've always been a fan of the 'Twin Mage' aesthetic, and given one half of that tends to be a Black Magic user...

Aetherial Manipulation: Attune to your targeted party member, traveling to their location. While within X yalms of this ally, they benefit from your Attunement and Leylines. Allies may end this by moving more than X yalms away. Only one ally may be attuned at one time.
Ice: Refreshes MP. (Ideally weaker than Song, but strong enough that it's more than 3% per 30 since you only spend a few ticks in Ice anyways.)
Fire: Increased Potency, Increased Resource Cost. (For when they want to pew pew and have resources to spare)

It's selective, so it can be stronger for the single individual. It also provides Black Mage a place in learning or in wipe recovery, where they can elect to deal less damage to feed MP into someone (And while B4 is still mostly DPS neutral, it does provide a non-wasted spell in Ice stance to give someone another tick of refresh) and progress further into a fight. Not as good as a Red Mage, but better than before, and rather than have a Flat party buff, the 'Fire' boost would also drain someone's TP/MP faster. Ideal for burn phases, less so for sustained DPS.

It's not truly "Raid buff", but it's a selective buff, which is acceptable on a cannon archetype.