Born in Tokyo, Japan, to an American couple, Lewis Gunn always felt out of place among his peers. Not only were his parents immigrants, but his father was also part of the military and traveled alot, often bringing back small souvenirs. Lewis' school days went by without any issues and he eventually joined the military, specializing in intelligence gathering.

Before joining the military, Lewis had no previous experiences with devils. His fellow officers told stories of how devils ruined their lives and how they joined the military because there was no other place to go. They also remarked it was easier fighting other humans than it was to fight a single devil. Lewis took none of this into consideration nor did he care enough. That was until a low level devil attacked his squad, slaughtering many of his friends and the surrounding camp. It was then that he realized how destructive devils really were. After that tragedy, he was honorably discharged from the military. Wanting to learn more about devils, he joined the Devil Hunter HQ in Tokyo and eventually founded the recon/intelligence division.

He’s hardworking and tends to be more focused on his job as a recon agent, taking it very seriously. This makes him a very efficient worker and climbed the ranks quickly, despite his aversion to talking and communicating with others. He finds making connections laborious and does not make small talk unless it’s part of his mission or job. He's a generally introverted agent and very obeservant. His face is rarely seen by the public, as he tends to stay back away from the actual capturing and killing of devils, though this does not deter him from occasionally fighting when the heads of HQ need him to.

As most agents in the devil hunting business, Gunn was required to form some sort of contract with a devil. During one of his recon missions, he attracted the attention of the Sound Devil; a devil that had been confined to earth until the next rebirth cycle. Unlike most devils, it prefers to be alone and is quite passive towards humans. It's usually seen drifting about deep in forests/marshes and near abandoned buildings. Gunn ended up forming a contract with the Sound Devil, agreeing to give his left ear in exchange to use some of the devil's powers and abilities.

He has a light skin tone with emerald green eyes and unnaturally grey hair despite his young age. His hair is short and fluffy, taking on the appearance of the bedhead style. He’s missing his left ear due to his contract with the Sound Devil, all that remains is a patch of dried blood that does not disappear. Lewis likes to wear things over his mouth, most of the time scarves or black surgical masks. His usual outfit, as well as devil hunting attire, consists of a black turtleneck, a white shawl-like cloak, gray combat pants, and black sneakers.