Tenma Asaboshi/Demons

Tenma, for as long as he can remembers, has fought countless Demons, and along the way, enslaved them using Demon Subordination Magic. The exact number is unknown, but Tenma has said that it is well below 100.

Formless Chaos, Seth
The Formless Chaos, Seth (無形乱セス, Muyōran, Sesu) is a Demon, said to have no physical form, due to his Curse. His appearance takes the form of a shadowy apparaition, with wolf-like characteristics, including claws, and face, and has two distinct red eyes.

He is a fearsome Demon, but lacks any true physical greatness that is considered "impressive" among Demons, but still above Humans. However, his greatest strength is his Curse, Eibito.
 * Eibito (影人, Shadow People): Seth's Curse allows him to manipulate "shadows", including himself. He compares his own body to that of a shadow, having no physical form when the Curse is activated, and is naturally weak to light-based attacks, but suffers no ill from the sunlight. The Curse can be compared to Shadow Magic in a sense. However, unlike Shadow Magic, Eibito can manipulate the shadows of individuals, even without coming into contact with them, and turn Seth in an intangible mass of darkness. Seth can also "possess" people, by first possessing their shadows, taking controlling of a human body as a host. There is no real time limit to how long he can stay in a human body, but while he is, he cannot use his Curse's full power, and only manipulate his own shadow. Seth has also shown the ability to control people, in a form similar to "puppetry", by controlling the shadows of people, he can control a person's every movement, telepathically, and with hand gestures if needed, and can do so to a number of people, but doing so requires a shadow to be present, as well as the target being weak willed to allow him to control them.

Eternal Serpent, Ouroboros
The Eternal Serpent, Ouroboros (限りない蛇ウロボロス, Kagirinai Hebi, Uroborosu) a female Demon with the lower body of a snake, and the upper form of a woman, complete with light purple skin, with tattoos on half her body, and elongated horns, with long white hair, that reaches below her waist, decorated with flowers. She also wears a rather revealing attire, revealing a large portion of her bust, and a small skirt on her waist.

Ouroboros is a very fast and agile Demon, her snake tail is also one big mass of muscles, allowing her to capture and crush people with ease, much like an actual snake does to its prey. However, she is more of a strategist than an actual combatant, exploiting her opponents weaknesses, and coming up with plans in order to better defeat them, which is the reason for why Tenma captured her, seeing her intellect as a valuable asset in Demon hunting.