Meccanical
Member
If you mean mechanically: It's a reskin of Vampire (which was basically Blue Mage), since that Job isn't available anymore due to plot events in Bravely Default. I have no idea why they decided on cat master (or vampire for that matter) to fill the role of Blue Mage.
I can kind of see Vampire being a blue mage because I guess you can kind of draw an analogy between stealing monster abilities and the supernatural talents of vampiric lore.
But Catmancer is just like...there's really no way to spin that.