A good demon in fiction is Gluttony from 'Fullmetal Alchemist'. Despite being one of the seven deadly sins, Gluttony has a certain child - like innocence. He follows orders but also shows moments of kindness. Another is D from 'Vampire Hunter D'. D is a dhampir, half - vampire and half - human, but his vampire side gives him some 'demonic' qualities. He uses his powers to fight against evil vampires, making him a kind of 'good demon'. Also, in the 'Shaman King' series, there are demons that are allied with the main characters, like Amidamaru. He is a spirit that has some demonic - like powers but uses them for good.
One good demon in fiction is Crowley from 'Good Omens'. He's a demon who has grown rather fond of Earth and its inhabitants over the millennia. He enjoys the pleasures of human life like fine wine and classic cars. Another is Alciel from 'The Devil is a Part - Timer!'. He's a demon who has to adapt to the human world and ends up showing a more likable and relatable side. Also, there's Mazikeen from 'Lucifer'. She's a demon with a complex personality, loyal to Lucifer and often showing a sense of honor in her own way.
In the world of fiction, Belphegor from 'Supernatural' can be considered a 'good' demon in some ways. He teams up with the Winchesters on occasion. He has his own motives, but at times his actions end up being beneficial to the main characters. Another example is Lailah from the 'Bayonetta' series. She is an angel - like being with some demon - like traits. She helps Bayonetta in her battles against the forces of evil. Then there's Pyrocynical from 'The Binding of Isaac' - related media. He is a character with demonic features but often plays a role that is not entirely malevolent in the game's lore.