Aki Hayakawa was a Public Safety Devil Hunter, working under Makima's special squad. He had contracts with the Curse Devil and Future Devil, and a former contract with the Fox Devil. He was killed and possessed by the Gun Devil, thus becoming a Gun Fiend. Aki Hayakawa is a handsome young man with medium-length black hair and green eyes. He usually wears his hair in a topknot style. He often wears the Public Safety Devil Hunter suit and tie. He also wears earrings and usually carries his sword on his back. After the Gun Devil took over his body, he becomes the Gun Fiend, his hair is let down with his eyes and forehead covered in dark veins. The barrel and slide of an M1911 is seen sticking out of his face in between his eyes with the gun’s hammer sticking out the back of his head, Aki’s left forearm is replaced with an M16A1. Aki generally appears to be a very stoic person. He acts mature and dependable when he's with his fellow Devil hunters, but is actually very soft when he is alone. He has a tendency to get attached to others easily, and hates to see people get hurt, especially his close friends. Unlike many of his associates, he is described by Himeno as being a "normal person", in the sense that he still grieves for those lost and has not become jaded enough to close his feelings off. Despite this, he is very determined and his primary motivation for killing the Gun Devil is revenge for his family. He is, however, entirely willing to put his own life on the line to save other people despite his own fear of death and even at risk to his ultimate goal. His air of cold detachment is actually a facade, and he has been seen to cry over the deaths of his comrades such as Himeno, and he grew to care for Denji and Power enough to try and forfeit his revenge goal in order to keep them safe.