An animation of chains
Of course, Sigel Knights have the conventional tank skills: that's pretty much the only conventional tank skill (unless you consider a ton of HP to be a skill, too). Well, hate is all about controlling the mob and making it hit what you want it to hit (the tank). Usually that means you run up to a mob, hit it with an agro skill, and then fight it there or let it follow you back to the party. In GD, the mob comes to you. When the Sigel Knight pulls, they are literally pulling the mob (or mobs!) towards them with an animation of chains that shoot out from the Knight's hand!
As the fight continues in close quarters, Sigel Knights can change the direction of the battle by switching between their different Auras. Getting walloped? Switch to Iron Aura and raise the party's defenses, or switch to Recovery Aura to boost healing and HP recovery effects. Getting swamped by social mobs hitting other party members? Switch to Challenge Aura and get their attention. Fighting but not tanking? Help your party does more damage by switching to Rage Aura, or help protect them from elemental attacks with Resist Aura. Overall, Sigel Knights take the tank class to the next level by maximizing their ability to control the situation and the fight, and by stepping up to help their party members immensely when needed.