Reincarnated Boss is a Manga/Manhwa/Manhua in (English/Raw) language, Action series, english chapters have been translated and you can read them here.
‘I will destroy my organization with my own hands.’ Lee Gangjin, the ultimate skilled gangster in the dark world. He is the most talented gangster with his fists he can rose to the top, but he is betrayed and killed by his most cherished younger brother, Jo Dooyoung. At that moment of death, he awakens in the body of high school student Lee Kangjin, who had ended his life due to being overwhelmed by school violence. Meanwhile, to maintain the regenarion the faction, the “Gangjin Faction” starts an “Underworld Audition,” and delinquent teenagers are enthusiastic about joining the Gangjin Faction. Filled with remorse, ‘Gangjin’ resolves to undo everything and personally eliminate the ‘Gangjin Faction’ he established.