Meikyuu Shinwa: Hajikete! Zack

Follow the adventures of Zack, a crazy boy with even crazier strength who loves to fight! What starts out as an innocent boxing match soon leads Zack into the world of invincible demon-possessed teenagers, acid-spewing mutants, and craven, bloodthirsty cultists! If you're looking for a manga that just bleeds insanity, then you've found it!

(Source: Golden Roze)