Leon is a failed red mage who constantly fails class changes - as a result, he acts as a support for his adventuring team, Wolf Fang Sword. Eventually, he is fired from the party for not being strong enough.

However, after leaving the team, Leon finds that he was stifled by his own team. The fact that he has a "Sage" class was unprecedented, and it turns out that he can fight perfectly fine on his own. Not to mention that his Sage class has a hidden power which only activates in certain conditions...

(Source: MU, edited)