Both are japanese dramas about delinquents and include a lot of comedy. In Densetsu No Head Sho, an ordinary guy pretends to be a delinquent. In Nanba MG5, a delinquent pretends to be an ordinary guy.
Both drama are about former bullied kids deciding for one reason or another to become delinquents and grow stronger. Also they all change their hair cuts because of that decision.
'Densetsu no Head Sho' might not be a BL but it's also about a guy who looks identical to the leader of a gang and finds himself temporarily taking his place!
