I Quit the Hero’s Party is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

There was once a party who sought to defeat the Demon Lord and save the world, the Hero’s Party. However, tired of the Hero’s Party unwillingness to go directly after the Demon Lord, the Ashen Wizard Raniel quit the Hero’s Party and returned to his hometown to meet with his master. There, he was recommended a position as an assistant professor at a prestigious academy. “Why are you so bad at this? Just make circuits, cover yourself in mana, and use it.” However, a genius like him didn’t seem to have any aptitude for teaching others… The strongest of mankind begins his hectic new job at the academy!