Rage

Rage is a form of power that manifests when you get hit or hit someone multiple times, and is one of the three magical categories. It is the newest of the three, and was discovered 300 years ago by Kaisellain.

Lore
Kaisellain discovered [Rage] by finding out that his home country, Tadaaki, was attacked and destroyed Esper, a neighboring country. Kaisellain was so angry that he did not sleep for 3 years, and managed to use his Rage as a weapon to destroy and raze Esper to the ground. Of course, his Rage was unrefined, and was more of a crude club compared to how Rage is used in the present.

It appears as a red bar in the middle of your UI, and you can use it to unleash Limit Breaks. Each character has different Rage multipliers. For example, the Warrior class has a 1.5x Rage multiplier, which means the Rage bar fills more quickly when playing as a Warrior.