As a Demon she has access to Hellfire and whatever her unholy magic manifest itself as. In her case her Hellfire is unsurprisingly average not really into the whole fighting concept. She prefers just to have people adore her and lust after her to increase her own power.
Miyuki sub-consciously releases a type of pheromone that increases the level of lust from people in in 5m vicinity she absorbs the pheromone in a 3 meter vicinity increasing her power by mere fractions, but she can consciously increase it to a 7m vicinity and absorbs at a 5m vicinity.
Of course there are limits, she can't take more then she can wield and when it tops off the ability cuts itself off.
Actively, once the pheromones are absorbed it is converted into demonic energies (demonic energies is a thing right?) in which she convert into a corrosive gas that at the cost of her power as a demon.
Siren’s Call- the ability in itself is nothing special, but it automatically makes her voice sound alluring to whoever hears it. Not only that, but when she sings it’s always perfect tone, pitch, note, you name it. This has the effect of increasing people’s desire of her, further increasing her passive ability.
The more energy she absorbs the more powerful her abilities become.