Hanzo Urushihara, also known by his original name Lucifer, is a fallen angel who was once a high-ranking archangel before descending into the demon realm and becoming one of the Devil King's four demon generals. He possesses a youthful appearance with purple hair and violet eyes, looking to be around fourteen to eighteen years old. He was born after the destruction of the angels' home world, making him part of the second generation of his kind, and he was once responsible for leading the archangels in heaven. Finding his existence in heaven too monotonous and boring, he abandoned his celestial duties, an act that caused him to lose his former status and gain black wings that signified his corruption into a fallen angel.

After leaving heaven, Lucifer traveled to the demon realm, where he eventually allied with the young demon lord Sadao Maou, then known as Satan Jacob. He was promised that the arrangement would be entertaining, and he famously gave Satan permission to kill him if he ever grew bored. He rose through the ranks to become one of the Four Demon Generals, leading the successful conquest of the western continent of Ente Isla alongside his new demonic comrades. It was during this campaign that he destroyed Sloan Village, the home of the hero Emilia Justina, which led to the death of her father. Sometime later, Emilia, having become the hero of Ente Isla, confronted and supposedly killed Lucifer by impaling him with her sacred sword.

However, Lucifer survived his apparent death due to the secret intervention of Olba Meyer, a corrupt archbishop of the Church of Ente Isla. Olba offered Lucifer a path back to heaven in exchange for allying with him to destroy both Emilia and the displaced Devil King. The pair followed their targets to modern-day Tokyo, where they hid in an abandoned school classroom. On Earth, Lucifer discovered that his demonic powers were greatly diminished, able to be replenished only by absorbing negative human emotions such as fear, despair, and pain, leading him to commit brutal muggings. He also quickly developed an aptitude for modern technology, becoming an expert hacker and a passionate enthusiast of video games and internet browsing.

His plan to eliminate both the hero and the demon lord ultimately failed, and he was defeated by a combined effort of Maou, Ashiya, and Emilia. After his defeat, Maou chose to show him compassion, taking him into his small apartment to prevent him from being discovered by the police for his crimes. Taking the human alias Hanzo Urushihara, he began living in what the residents call Devil's Castle, where he was provided with a laptop and internet access by Maou with the nominal task of researching magic, though he primarily uses the connection to play online games and make frivolous purchases that put a strain on the household's already meager finances.

Urushihara's personality is defined by his profound laziness, apathy, and reclusive nature, which has led those around him to frequently label him a hikikomori or NEET, much to his irritation. He is cunning and manipulative, as shown when he tricked Maou, Ashiya, Chiho, and Emi into retrieving his forgotten gaming console from a deserted classroom under the false pretense of a magical investigation. He prefers to spend his time surfing the internet, playing video games, eating junk food, and complaining rather than contributing to any household responsibilities or assisting with research. Despite this nonchalant and carefree facade, he occasionally displays a more serious and selfless side, such as when he sold his hard drive to help the household settle a debt, an act that ultimately made their financial situation worse. While he appears childish and petty, his detached demeanor hides a desire to protect the fragile and comfortable routine he has established for himself in the human world, and he will go to great lengths to ensure that his gaming-centric life is not disturbed.

In his new living arrangement, Urushihara has dynamic relationships with the other characters. He shares a complex history with Sadao Maou, having once served as his general before betraying him; after being taken in, Maou displays a degree of friendly patience toward him that is often tested by Urushihara's wasteful spending and laziness. He is frequently the target of nagging from Shirou Ashiya, who criticizes his lack of gratitude, his disrespect toward their master, and his habit of wasting money on expensive goods. His interactions with Emilia Justina, who now goes by Emi Yusa, begin with hostility but gradually evolve into a surprising and humorous reluctant camaraderie, with their shared experiences in the human world slowly chipping away at their initial animosity despite their underlying tensions and deep-rooted resentments. He is also the son of Ignora, who experimented on him while he was still in her womb and made him immortal, and his father is Sataniel.

As a fighter, Urushihara possesses several notable abilities, even in his weakened state on Earth. He can summon his signature black wings to fly at great speeds. He is capable of creating explosive projectiles of demonic energy, and the feathers from his wings themselves can be detonated on command to create destructive explosions. He also possesses heightened endurance, having survived powerful magical attacks from both Maou and the sacred sword of Emilia. On the rare occasions when he consumes food infused with holy energy, his original white angelic wings and holy magic are temporarily restored to him. In addition to his combat powers, he is exceptionally skilled with technology, able to quickly master and hack various electronic devices and computer systems with ease. Despite his supernatural origins, Urushihara is plagued by several unusual mundane quirks, including allergies to dust and cats, as well as motion sickness when traveling in long-distance ground vehicles.