Limit Break

Limit Break (限界突破) is a term coined for the condition where someone breaks off his/her abilities' limits.

Description
A condition where someone can transcend from their original abilities to a higher level. But for some reason, normal humans are never eligible to have a limit break. Thus, making them to be someone who can defeat the demon lord. limit break's concept doesn't apply to the heroes.

Expectation
Even though it said humans other than the hero can't have their limit break, Rein Shroud already seems to break all of his shackles to reach the limit break. This was triggered due to taming a demi-human from Cat Tribe, Kanade. Each time he tames the other strongest race, he not only gains their abilities but also gets closer to his limit break phase. Kanade said that the more he tames the strongest races the more he'll get stronger and ultimately be able to defeat the demon lord.

Trivia

 * Rein Shroud is presumably the first person to have a limit break other than a hero.