Vivian is a major character in Paper Mario: The Thousand-Year Door. Vivian originally worked as a member of the villainous Shadow Sirens alongside her sisters, Beldam and Marilyn. Later, Vivian defects from the Shadow Sirens and joins Mario as his fifth party member. Although she suffers from an inferiority complex, throughout the events of the video game, Vivian's character develops as she learns to respect herself.
There is debate on her gender as Beldam insults her by calling her a man in the Japanese version. The tattle log also says she is the "youngest sister er... brother." Though due to the use of she and her after the insult it is most likely one of the many "Paper Mario jokes" that Mario took the insult seriously. It is most likely an insult due to Vivian being the prettiest sister and the joke wouldn't get translated the same way.