Vivian is the youngest sibling of the three Shadow Sirens and formerly one of the major antagonists in Paper Mario: The Thousand-Year Door. Unlike her sisters, Vivian is kind, compassionate, and gentle in her interactions with other people. Vivian and her sisters seem to have been somehow related to the Shadow Queen prior to the queen's imprisonment, though the nature of this relationship is unknown. She is consistently put down by her oldest sister, Beldam, and has had a poor relationship with both her sisters for quite some time when Mario meets her; this poor relationship has led to her having a deep-seated inferiority complex and is part of the reason she joins Mario. She is also considered the cutest of the Shadow Sirens, much to the chagrin of her elder sisters.

Vivian was introduced as a party member in Chapter 4 and is the fifth character to join Mario's party in Paper Mario: The Thousand-Year Door.

Apart from her role in the game, Vivian is also well known for being depicted as a trans woman in the original Japanese release of the game and several of the other localizations. In the 2024 remake, much of the dialogue surrounding Vivian was rewritten to more overtly refer to Vivian as a transgender woman in the English translation of the game as well.