Going with the idea that it's casting-looking gear the character in question is wearing, while acknowledging how similar that weapon looks to a dagger of some kind... On the off chance that they would add a class/job simply with a patch, I'm gonna throw RDM (Red Mage) on the table. In FFXI, one of RDM's main weapons was a dagger, in fact they were just as good with them as they were with swords, and could even equip the Relic dagger.

If it can be THF with mage-looking gear on, I think RDM is a good Possibility...