The siren originates from Greek Mythology, you know, the stories about Zeus and the Olympian gods. A siren is a half bird-half woman. We already have four playable sirens, that is: Lilith, Maya, Angel and Commandant Steele. That leaves two other female playable characters available in Borderlands 3. In the Four Assasins mission in Borderlands 2 we confirm that there can only be 6 sirens at one time in the Borderlands world and in my opinion, we will have two more sirens. I don't think Tiny Tina will be one of them though. It would be cool to have her as a playable character.