Blue Mage tank. It would be a vengeance based tank that juggles between cooldowns that reduce damage, and cooldowns that increase received damage to be used to fuel a vengeance based ability. I envision something of a reversed Wildfire: 10% of all damage taken over 10 seconds gets returned all at once, with an animation taken at random from the boss or mob attacking the tank. Main weapon? I don't know at the moment, I'm told a fencing sword is how BLUs usually operate.