[Lord Semaj]

I was actually watching a series called Mahou Sensei Nejima, and they had a take on the role of a tank.

Okay, so in the show, every mage has a fighter that assists them. Mages are not only physically weak, but they can't cast any spells if you just interrupt them with a bonk on the head or flick their forehead or anything. So the fighter has to ward off physical attacks that might interrupt the mage so he can unleash his great power. Well, that's what Vanguard seems to be doing. Not sure if melee classes will have spell interrupt abilities, but we'll see. Still, the mage definitely had the "aggro" being the strongest opponent, he just had a very large weakness that the fighter could help defend against. When two mages met, their fighters would each try to interrupt the other mage while defending their own, leading to fighter vs fighter battles while the mages supported with spells.

Leads to exciting battle, much better than just Aggro-lock, where you can choose to support the tank by attacking his enemy or target the enemy mage with your own spells.