“Underboss (also capo bastone or sotto capo) is a position within the leadership structure of Sicilian and American Mafia crime families. The underboss is second in command to the boss. The underboss is sometimes a family member, such as a son, who will take over the family if the boss is sick, killed, or imprisoned.” [Underboss – Wikipedia] goo.gl/jQmMp4
“mook Usually used to refer to generic goons in TV and role-playing games. Mooks are usually faceless henchmen who show up only to be easily dispatched by the main characters.” [Urban Dictionary: mook] goo.gl/Im85L
“In the yakuza’s society, 兄貴 is used to address a senior you work with (replacement of 先輩[sempai])” [兄貴[aniki] | Japanese words of anime fans, by anime fans, for anime fans] goo.gl/K8bfsH