This is Dearg Due, a succubus from the realm of Mag Mell, who is the greatest worry of the demon lord Balor of Mag Mell a demon with a conscience. Balor created his horde from the matter of his shadowlands, he created Caoranach who would sculpt and create all of his other demons. The first demon was Dearg Due, a succubus, who stalked the land draining the life energies of humans. She was Balor's favorite and trusted acolyte for centuries.
It was always a danger to all demons that walked the Earth, that they would develop feelings toward humans. Various demons have taken mates of humans. While as a demon lord Balor knows this happens, he still has to crush and destroy the deserters.
Unfortunately Dearg Due has developed what none of residents of Mag Mell had, a conscience. Dearg Due killed a teenage runaway, then discovered the runaway had a baby. Then for some reason Dearg Due did not drain the baby's life energies and took it with her. There is a saying "the road to Hell is paved with good intentions" and where does the road pave with bad intentions lead? Then she kept it live and left the baby to be found by humans. She let the baby to live. The baby was Leanan Sidhe and has grown into a teenager.
Then this was the first of many inexplicable decisions she would start to kill only seemingly evil or bad people. This became fewer and fewer as she saw that "bad" people also had good traits. Now she always drains the life energies to keep herself alive. This is what worries Balor there is no one event that causes this change in one his very loyal servants. Is this the fate for all of his demons.
She continues to watch Leanan Sidhe from a far, Dearg Due does not have any contact with her.
This was adoptable of :iconnoodles919: of a very beautifiul yet deadly succubus. This is my take on her.