Dorohedoro

Publisher's blurb:

Once upon a time, there was the first devil, Chidaruma. He simply came into existence on his own. He was omnipotent, omniscient and the master of his own dimension. Feeling lonely one day, Chidaruma created the sorcerers to amuse him. When they multiplied and got too impudent, he created a world to separate himself from them, but also gave them masks and trained some of them to become devils like him.