My job concept is around this.

Gunblade would have a unique action type, the Weaponspell.
Weaponspell: Instant cast if melee range, increasing cast time the farthest is the target, up to 25y.

And has a unique trait that increases magic damage every time a weaponspell is used, up to 4 stack, then release in the next spell. Normal spells have low potency, but with the 4 stack they become stronger than the weaponspell.

You can check it here: http://forum.square-enix.com/ffxiv/t...V-Original-Job