Vivian is the youngest member of the Shadow Sirens, three siblings who serve as Grodus' henchwomen. Vivian is constantly berated by the oldest sister Beldam, which led her to develop an inferiority complex. In Twilight Town, she agrees to help out Mario after his name was stolen by Doopliss, and fights alongside him from then on against her own sisters. However, she was unaware she was helping Mario at first due to his identity being taken away, and when she found out, she leaves him, but then shortly rejoins him after thinking it over and realizing that Mario was the only person that had ever been nice to her. In the field, Vivian is able to hide Mario by pulling him into the ground, hiding him from any nearby enemies and allowing them to travel under some fences and dodge spikes. In battle, Vivian is skilled with fire attacks and is able to hide Mario from enemy attacks.
Difference between Japanese and North American versions
A commonly known fact among Mario fans is that in the Japanese version, Vivian is actually male, and that he cross-dresses as part of his efforts to earn the approval of his sisters. In the game, Vivian kisses Mario in the cheek in one scene and shows affection towards him. To avoid controversy, Nintendo of America flat-out changed Vivian's gender to female for the North American version.