Convergence is a Merit ability for Blue Mages. It increases the power of the next Blue Magic spell at the cost of that spell only affecting one target. Single-target Blue Magic spells are boosted with no drawback.
Convergence is an Arcanist ability learned at job level 9, and costs 3 slots to equip. It increases the damage of magic that can only be group-cast to 1.5 times normal by narrowing its focus to a single target.