Siren is a slender, scantily clad human looking figure. She has blond hair and carries a golden harp, and wears dark blue clothing.
Siren has a history of censorship in localized versions of Final Fantasy VI, as her original Japanese Super Famicom sprite depicts her with her rear uncovered. The western Super NES release added shorts or a skirt to cover her, but the Playstation port of the game used all original Super Famicom sprites, including the uncensored Siren. The Gameboy Advance port gave Siren a sprite censored in a different manner, with a strip of cloth over her rear that does not cover her as much. The iOS and Steam port gives Siren a sprite based on the original Super NES sprite, giving her what is more clearly a short skirt with slits on the sides, and this sprite is used in both the Japanese release and the western release.
Siren was one of several espers captured by the Gestahlian Empire during their first raid on the esper world. The captive espers were taken back to the Magitek Research Facility at Vector and experimented on and their magic drained to develop the Empire's Magitek army.
At an unknown point, Ramuh attempted escape with Siren, Kirin and Cait Sith, but only Ramuh survived. He kept the magicite remains of his comrades with him as he went into hiding at Zozo. When the Returners met Ramuh while searching for Terra, Ramuh urged them to shut down the Magitek Research Facility and free the espers still held captive. To aid them in this, he turned himself into magicite and entrusted himself and the three magicites of his comrades to them.
Siren costs 16 MP to summon and casts Lunatic Voice (Hope Song in the Super NES and Playstation versions), which inflicts Silence on all enemies with a hit rate of 136. At Level Up, she provides a +10% boost to HP.
Siren is not very useful as a summon. The party will not often come up against groups of enemies that use magic prominently and are vulnerable to Silence, and for single enemies the party can simply cast the Silence spell Siren teaches. She has some utility in the Cultists' Tower, where a fair number of enemies are vulnerable to Silence and can only use magic, and Siren costs little MP to summon and bypasses the innate Reflect status many enemies have. Her HP bonus is entirely useless, offering a very minor boost and other espers in the game offer a larger one.
Siren is very useful as an early magicite. The status spells she teaches have some use throughout the game, and Fire is the only offensive spell the party can learn aside from those taught by Ramuh, until they acquire Ifrit and Shiva in the Magitek Research Facility.
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.