I'd imagine it'd be a combination of FFT with some FF7 Remaster like flare, but that might be stepping to much on the coat tails of the latter, having a job directly inspired by their most popular game to date. Yes I am aware Gunbreaker borrows heavily from Squall's Gunsword Style. to be honest, if it had to exist, I'd almost suggest it be a charging burst DPS job, and by charging I mean long casting times in its burst mode much like a wizard, and weaker but limit gauge(burst) recharging stance/style also like wizard's ice mode. You'd build up one level of limit per building stance skill used and attacks would cast faster in this stance, but when you did switch to Limit Breaker stance, you'd have longer cast times but the damage would be well worth it, not to mention you'd have a bit of damage reduction so that the long cast times have a trade off in that you're a mini tank, able to shrug off 20% of damage taken while charging an attack in Limit Breaker stance.