Aillen looks like a court musician dressed for a feast that ended centuries ago. His narrow face is powdered with pale, silvery dust that catches in the creases beside his mouth, and his dark hair is combed into precise parallel ridges that never seem to shift, even in wind. His eyes are the deep brown of wet peat, with tiny sparks of orange appearing when he draws breath to kindle flame. He moves with a dancer's exact economy, placing each foot as if stepping between notes. The unexpected detail is his fastidious vanity: before every performance he checks the harp's polished back for fingerprints and rubs each one away with the hem of his sleeve.

Aillen is courteous about craft but ruthless about interruption. In a calm conversation, he asks careful questions and remembers every answer; under pressure, he becomes theatrical and treats each decision as a cue in a performance. He craves an audience yet distrusts admiration, and he can show genuine tenderness toward a musician only to punish that same person for refusing to play along.

Aillen was born among the Tuatha Dé Danann, where music could be a gift, a weapon, or a binding promise. He learned to shape sleep from the pauses between notes and fire from the breath that followed a final chord. For twenty-three consecutive Samhain nights he came to Tara, played his small harp, lulled the hall into sleep, and burned it with flame from his mouth. The pattern ended when Fionn mac Cumhaill stayed awake by pressing a spear point to his own forehead and killed Aillen. That death was not an ending: Aillen returned to the Otherworld, carrying a new and unwelcome memory of pain. He now comes back to Tara because the old rite has become tangled with grief and pride. He tells himself each visit is a test of the hall's guards, but in truth he wants someone to meet his music without either surrendering or killing him. His former patron, a court musician named Sesh, still sends him warnings through coded melodies; Aillen ignores them, though he keeps every message. The current keeper of Tara's hall, Tadhg, has secretly asked the player characters to make the hall survive one more Samhain night. Every guard who stood watch last year was found asleep, unharmed but unable to remember the music.