I'd add a few single mana spenders, as well as a few conditions that allow more accelerated mana gains. The goal is to build towards your big pay off while also using the single mana spenders for impactful effects.

Berserk
Ability
Recast: 45 seconds
Cost: 25 Black Mana
Effect: Grant the target party member 'Berserk', increasing their damage dealt and their Resource Costs by 20% for 20 seconds.

Refresh
Ability
Recast: 45 seconds
Cost: 25 White Mana
Effect: Grants the target party member Refresh, restoring their TP and MP for 15 seconds.

Impact: Impact gains a trait based on the spell cast prior to it. Impact no longer requires Jolt to be cast and no longer generates Mana on its own.
-Scatter: Impact deals 40% less damage but hits all targets within 5y of the primary target. Generates 3/3 Mana.
-VerFire/Thunder: Impact generates 8 Black mana and increases further black mana gains by X% for the next 20 seconds. Overrides the White mana generation boost.
-VerStone/Aero: Impact generates 8 white mana and increases further White mana gains by X% for the next 20 seconds. Overrides the Black mana generation boost.
-Verflare: Impact grants you Berserk for 20 seconds.
-VerHoly: Impact grants you Refresh for 15 seconds.