Flute with a siren's power dwelling inside.
Siren's Flute is the second strongest weapon for Eiko, providing 30 Attack and teaching the abilities Full-Life, Dispel, and Esuna. It can be bought for 7,000 gil at Black Mage Village (disc 4) or stolen from Lich.
The Siren Flute is a wind instrument equippable by a level 23 Bard. It adds +2 to the effect of Foe Requiem songs. (For each additional "plus" after the first, the requiem effect gains a +10% bonus to its duration and a +1 point of damage per Tick do the damage over time effect.) It is obtained through completing the Bastok quest "Lovers in the Dusk".
Sirens are from Greek mythology. In the story of Odysseus, the Sirens are beautiful women who lure sailors with their voices. Odysseus escaped the Sirens by having all his sailors plug their ears with beeswax. He was curious as to what the Sirens sounded like, so he let himself be tied to the mast to ensure he could not fall victim to their voices.