siren is a GIRL lol, and casts silence on all the enemys but most bosses and hard enemies will be immune. it does damage 2 but very little.

though to be honest all the gfs by the end of the game except eden, cerberus and doomtrain will be of little use in battle. but you need them to master the game,

plus u should get at least 6 to keep your characters junctioned all at once, and the best gfs give wicked junction abilities for your characters in terms of stats and status/elemental protection, as well as refining those cards into items