The ghastly lovechild between Ursula and Bianca Castafiore, Cylostra Direfin is a Legendary Lord of the Vampire Coast faction in Total War: Warhammer II and a newcomer to the Warhammer Fantasy world, created by CA.
Cylostra Direfin is an undead ghost of the Banshee type who was once a Bretonnian singer who enjoyed vast popularity and prestige among the knightly nobles, sociopathic diva-tendencies aside. She was meant to sing for the Phoenix King in Lothern as a part of a diplomatic mission, but on the way her ship was caught in a storm. The captain attempted to steer clear of it but Cylostra, filled with hubris, pushed him overboard and took control of the ship while singing that her voice would make the winds and waves bow to her. Unsurprisingly, the ship sank while Direfin's beautiful voice echoed over the tempestous sea.
It wasn't the end for lil' Cyllie though - Before her death, a malign being (heavily implied to be Mannaan's edgy Stupid Evil split personality Stromfels) contacted her and proposed a deal - Serve him in unlife as his Siren of the Storm, and she would be given the power to finally sing for the Phoenix King... At the bottom of the ocean. Being an insanely self-absorbed diva, she accepted. Now she roams the seas, dragging down any ship she comes across with undead sailors and oceanic magic, bolstered by her ethereal voice.
And yes, there was a small shitstorm over the inclusion of a new character not created by Games Workshop, which wasn't helped since that character is a portly woman... And that's all we're going to say about it.