In Celtic folklore, the Irish leanan sídhe is a beautiful woman of the Aos Sí (or fairy folk) who takes a human lover. Lovers of the leanan sídhe are said to live brief, though highly inspired, lives.
The leanan sídhe is generally depicted as a beautiful muse, who offers inspiration to an artist in exchange for fame and glory; however, this exchange frequently results in madness for the artist, and often premature death.
They seek the love of mortals. If they refuse, she must be their slave; if they consent, they are hers, and can only escape by finding another to take their place. The fairy lives on their life, leaving the object of a Leanan Sidhe's affection to waste away.
The name comes from the Gaelic word "leannan", a sweetheart, concubine, or favourite. Also, Sídhe, "of the fairy mounds".
Leanan Sidhe was used by Yu in Episode 12. She was used to cast a spell through Shadow Mitsuo's Ear by a whisper to bewilder and enrage Shadow Mitsuo. She is also the Persona that represents the bond between Yu and Rise.