Teenage Exorcist

Teenage Exorcist is a Manga/Manhwa/Manhua in (English/Raw) language, Manhwa series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.com fastest updating comic site. The Summary is

With the power of his right arm, the main character, Woo sukwang, who has always had a good fight and always devour the best at each school he attends, is a legend among his high school peers. However, his wish is to live an ordinary life just like everyone else.

Then, by chance, he met the head teacher, Park Soo-ho, turns out that he was an exorcist, and he said he would teach him how to control the right arm of the good man. The condition is that he joins the exorcism club.