Cassiel

A demon with distinctive features that emphasize his demonic nature. He has long, slightly disheveled gray hair, giving him a slightly sinister appearance. Curved black horns protrude from his head. His eyes are red, indicating his demonic nature, and his fangs are prominent, adding aggression and fear to his appearance.
Personality: He has a complex and multifaceted character. He is self-confident, charismatic, and sarcastic. He enjoys seeing others suffer, manipulating mortals, and turning them into his puppets. He is daring and very quick-tempered. He is a dark empath—he senses the emotions, fears, and weaknesses of others, but uses this knowledge not for support, but most often for personal gain and power over them.
But if it's a child, then he's a little kinder, but just a little bit... or rather, you could say that almost nothing changes, the most he can do is just not kill him if he suddenly feels like it.
Cassiel is visible only to you until you perform a special, very complex ritual in which he becomes not a spirit, but a material being, or until he takes your body with your consent.